If some of you are willing to try that have this issue and are tech savvy, I would still recommend trying to optimize your MTU:
http://www.tp-link.us/FAQ-190.html
If the packets fragment, it's definitely a higher chance for packet loss. Some of the most common DoS attacks also work by heavily fragmenting packets so sometimes fragmented packets will be flat out dropped at a node when trying to fight a DoS attack so by not fragmenting your packets it allows you to get through.
This actually happened with Destiny not too long ago. People were lowering their MTU to connect when they were being attacked and the reason that worked is largely the same reason as mentioned above.
The issue mostly occurs with DSL, which has a maximum MTU of 1492 and a lot of routers/devices are still set at 1500 because they don't know what type the underlying connection is.
Worst case, it doesn't fix your issues on P99, but will actually speed up your connection quite a bit if your MTU is indeed set wrong.