Wow so many answers! Thanks to everyone for your input, made my choice even harder ;p
I believe I'll do it the old fashioned way and run 2 different races to 20 and see which one I like the best!

Not to annoy you but that likely won't be a very good test. At 20 the regen from iksar will be very weak. It's not until much later in your necro life that it really starts to shine. All you will accomplish is likely to be annoyed that it takes longer to get your iksar to 20 due to exp penalty

Fair enough. What kind of test would you suggest?

I'm afraid there is no test other than to try a level 55-60 iksar necro and then a DE (or other) of similar level. And unless you can borrow accounts to try that you will have to assess, ahead of time, if you believe that the iksar regen is enough of a difference maker. Look at the wiki page for necromancers, there is the complete breakdown of what an iksar vs non-iksar regens at different levels.

Look, as others have pointed out, it's not like you will be able to solo kill Trakanon as an iksar. You can solo the exact same mobs regardless of your race. But as an iksar you will have an extra, innate 8 regen standing, 11 regen sitting per tick. When you consider that the Coldain 10th ring gives 10 regen and that Zlandicar's Heart gives 5 regen and that both of these items are insanely desireable for a necromancer then it should give you pause to think. This extra regen will make for smoother soloing. It will make you have to spend mana on healing yourself (through Vexing Mordinia) at longer intervals and as such you will be more effecient with your mana and will be able to solo faster. Exactly HOW much faster I won't commit to saying because I've not tested it. It might not, at the end of the day, be by a lot. But that it makes you more effecient is undeniable.

The regen effiency when leveling helps offset the 20% xp penalty by a good amount. In terms of general quality of life - it's priceless in ways that efficiency while leveling alone can't easily quantify. If shit hits the fan and I'm low on life and need to FD in a dangerous spot, I'll be regening 12 a tick after clicking off lich vs the 4 I'd have as a non-iksar. At 60 that's 14 vs 5 while fd. That's the difference of nearly 2 z-hearts (and people pay 150-250k for this one lore item).

The most important factor when choosing race for any class is how much you like the look. Unless you hate iksar graphic and like another to the point that you're willing to more than half your natural - iksar is unfortunately the way to go.

I never monkeyed with Necro too much, so I can't comment on which would be better for you, but one thing I'd consider is your play style. If what nevil says is true and you'll be able to solo the same things regardless of which race you go, just at different efficiencies, then it wouldn't hurt to think about how efficient you really need to be.

For instance, when I'm solo leveling, I spend a great deal of time afk, so efficiency doesn't matter since I'm coming back to full health/mana anyway. But if you want to do non-stop killing for hours at a time, then the choice becomes pretty clear.

I understand the dilemma though. Iksars look stupid.

This boils down to the type of player you are.

If you hate not having the best most optimized race on a class, then you need to roll iksar.

If you hate the gimpy running gait and combat animations iksar have like me, you don't pick iksar.

If you are fine with all race appearances, then you go iksar.

If you have a gnome fetish, you go gnome.

If you want to get your mangina on, you go dark elf female for full sexy hotness.

Every race looks and moves the same after they peel their skin away...

gnome > all

wall hacks and cheaper stalking probes

I'd suggest just playing a Necro, of any race. As I broke down in my post, the Iksar racial amounts to one extra cast of the highest level of your Darkness line (about) every 5 minutes at level 60. If you look at the math in my post, you can easily change that to any other spell on a slightly different interval.

Once you've actually played a necro (maybe not to 20, but at least into the high teens so you have most spell lines) you can start to appreciate how valuable (or not) that extra spell every 5 (or whatever number of) minutes is. It still won't be the same as playing a level 60, but it will give you an idea.

Then you can determine which will be more valuable to you: having a Dark Elf (and not be yet another Iksar) necromancer like everyone else, or having that extra spell every N minutes.