So after hearing rumors that epic haste does not effect backstab as worn haste should, i went to test some things. It did seem that epic haste was not effecting it as it should so i decided i'd do a study. During that test study i realized that it also seemed that the 27% haste seemed to be doing the same level of effectiveness as the 41% haste. So i took some logs.
HYPOTHESIS ONE: Epic Haste does not effect backstab refresh timer.
TEST ONE: No Epic, No worn haste, no buffs, 5 data sets.
[Thu Sep 01 00:49:10 2016] You try to backstab Manasana, but miss!
[Thu Sep 01 00:49:10 2016] You try to backstab Manasana, but miss!
[Thu Sep 01 00:49:20 2016] You try to backstab Manasana, but miss!
NO EPIC 1= 10 seconds
++++
[Thu Sep 01 00:54:35 2016] You backstab Manasana for 185 points of damage.
[Thu Sep 01 00:54:35 2016] You backstab Manasana for 138 points of damage.
[Thu Sep 01 00:54:45 2016] You backstab Manasana for 254 points of damage.
[Thu Sep 01 00:54:45 2016] You backstab Manasana for 167 points of damage.
NO EPIC 2= 10 seconds
++++
[Thu Sep 01 00:55:14 2016] You backstab Manasana for 237 points of damage.
[Thu Sep 01 00:55:25 2016] You backstab Manasana for 142 points of damage.
[Thu Sep 01 00:55:25 2016] You backstab Manasana for 137 points of damage.
NO EPIC 3= 11 seconds
+++
[Thu Sep 01 00:57:38 2016] You backstab Manasana for 147 points of damage.
[Thu Sep 01 00:57:38 2016] You backstab Manasana for 157 points of damage.
[Thu Sep 01 00:57:46 2016] You backstab Manasana for 223 points of damage.
NO EPIC 4= 10 seconds
++++
[Thu Sep 01 01:43:15 2016] You try to backstab Manasana, but miss!
[Thu Sep 01 01:43:25 2016] You backstab Manasana for 146 points of damage.
NO EPIC 5= 10 seconds
Mean: 10.2
Median: 10
Mode: 10
TEST TWO: Epic, No worn haste items, no haste buffs, 5 data sets.
[Wed Aug 31 17:53:01 2016] You backstab Morvahl for 358 points of damage.
[Wed Aug 31 17:53:11 2016] You try to backstab Morvahl, but miss!
[Wed Aug 31 17:53:15 2016] You say, 'NO BELT'
NO BELT 1= 10 seconds
++++
[Thu Sep 01 00:34:53 2016] You backstab Manasana for 127 points of damage.
[Thu Sep 01 00:34:53 2016] You backstab Manasana for 193 points of damage.
[Thu Sep 01 00:35:03 2016] You backstab Manasana for 139 points of damage.
NO BELT 2= 10 seconds
++++
[Thu Sep 01 00:47:02 2016] You backstab Manasana for 178 points of damage.
[Thu Sep 01 00:47:02 2016] You backstab Manasana for 454 points of damage.
[Thu Sep 01 00:47:12 2016] You try to backstab Manasana, but miss!
NO BELT 3= 10 seconds
++++
[Thu Sep 01 01:12:01 2016] You backstab Manasana for 449 points of damage.
[Thu Sep 01 01:12:11 2016] You backstab Manasana for 194 points of damage.
[Thu Sep 01 01:12:11 2016] You backstab Manasana for 324 points of damage.
NO BELT 4= 10 seconds
++++
[Thu Sep 01 01:12:32 2016] You backstab Manasana for 174 points of damage.
[Thu Sep 01 01:12:42 2016] You backstab Manasana for 468 points of damage.
NO BELT 5= 10 seconds
Mean: 10
Median: 10
Mode: 10
HYPOTHESIS ONE CONCLUSION: The Rogue epic does not effect backstab refresh timers.
HYPOTHESIS TWO: Worn haste items above 27% do not increase backstab refresh ratio.
TEST ONE: Runebranded Girdle (27% worn haste), No haste buffs, no other worn haste, 5 data sets.
[Wed Aug 31 17:51:11 2016] You backstab Morvahl for 372 points of damage.
[Wed Aug 31 17:51:11 2016] You backstab Morvahl for 194 points of damage.
[Wed Aug 31 17:51:20 2016] You backstab Morvahl for 303 points of damage.
[Wed Aug 31 17:51:33 2016] You say, 'Runebranded Girdle'
RBG 1= 9 seconds
++++
[Thu Sep 01 00:32:11 2016] You try to backstab Manasana, but miss!
[Thu Sep 01 00:32:19 2016] You backstab Manasana for 123 points of damage.
[Thu Sep 01 00:32:27 2016] You say, 'Runebranded Girdle'
RBG 2= 8 seconds
++++
[Thu Sep 01 00:45:53 2016] You backstab Manasana for 174 points of damage.
[Thu Sep 01 00:45:53 2016] You backstab Manasana for 194 points of damage.
[Thu Sep 01 00:46:01 2016] You backstab Manasana for 271 points of damage.
RBG 3= 8 seconds
++++
[Thu Sep 01 01:06:06 2016] You backstab Manasana for 186 points of damage.
[Thu Sep 01 01:06:14 2016] You backstab Manasana for 219 points of damage.
RBG 4= 8 seconds
++++
[Thu Sep 01 01:20:47 2016] You backstab Manasana for 474 points of damage.
[Thu Sep 01 01:20:55 2016] You backstab Manasana for 392 points of damage.
RBG 5= 8 seconds
++++
[Thu Sep 01 01:06:06 2016] You backstab Manasana for 186 points of damage.
[Thu Sep 01 01:06:14 2016] You backstab Manasana for 219 points of damage.
RBG 4= 8 seconds
++++
[Thu Sep 01 01:27:43 2016] You backstab Manasana for 195 points of damage.
[Thu Sep 01 01:27:51 2016] You backstab Manasana for 170 points of damage.
[Thu Sep 01 01:27:51 2016] You backstab Manasana for 152 points of damage.
RBG 5 = 8 seconds
Mean: 7.8
Median: 8
Mode: 8
TEST TWO: Renard's Belt of Quickness (41% worn haste), No haste buffs, no other worn haste, 5 data sets.
[Wed Aug 31 17:52:01 2016] You backstab Morvahl for 301 points of damage.
[Wed Aug 31 17:52:01 2016] You backstab Morvahl for 185 points of damage.
[Wed Aug 31 17:52:08 2016] You backstab Morvahl for 209 points of damage.
[Wed Aug 31 17:52:15 2016] You say, 'Renard's Belt of Quickness'
QUICKNESS 1= 7 seconds
++++
Thu Sep 01 00:33:36 2016] You backstab Manasana for 139 points of damage.
[Thu Sep 01 00:33:36 2016] You backstab Manasana for 169 points of damage.
[Thu Sep 01 00:33:44 2016] You backstab Manasana for 166 points of damage.
[Thu Sep 01 00:33:44 2016] You backstab Manasana for 408 points of damage.
QUICKNESS 2= 8 seconds
++++
[Thu Sep 01 00:43:56 2016] You backstab Manasana for 437 points of damage.
[Thu Sep 01 00:43:56 2016] You backstab Manasana for 235 points of damage.
[Thu Sep 01 00:44:04 2016] You backstab Manasana for 427 points of damage.
QUICKNESS 3= 8 seconds
++++
[Thu Sep 01 01:06:54 2016] You backstab Manasana for 260 points of damage.
[Thu Sep 01 01:07:02 2016] You backstab Manasana for 158 points of damage.
[Thu Sep 01 01:07:02 2016] You backstab Manasana for 203 points of damage.
QUICKNESS 4= 8 seconds
[Thu Sep 01 01:13:13 2016] You backstab Manasana for 472 points of damage.
[Thu Sep 01 01:13:13 2016] You backstab Manasana for 472 points of damage.
[Thu Sep 01 01:13:21 2016] You backstab Manasana for 305 points of damage.
QUICKNESS 5= 8
Mean: 7.8
Median: 8
Mode: 8
HYPOTHESIS TWO CONCLUSION: Worn haste items above 27% do not effect backstab refresh any differently than a 27% worn haste item would.
Auxiliary findings: It appears to me that it is a good idea to have a haste belt as a rogue with our current coding. The increase in backstab damage is roughly 20%. Because rogue damage in general is 40% of the rogues overall dps, there is no better belt outside a worn haste belt--assuming the rogue is not using some other form of worn haste.
**this test did not include stacking worn haste items nor worn haste items in slots other than belt slots.