I think the real question is..why wouldn't you pick Iksar? It has a clear advantage. The only reasons I can think of would be that Iksar is hated everywhere or aesthetics. Necro is also hated most places anyway and I think a lot of Necro gear has -CHA stats so you might as well embrace the hatred and benefit from it by going Iksar.
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If it's just the aesthetics that you don't like and it's enough to make you not roll an Iksar then the benefits don't matter anyway so just pick which one you like the look of best.
I guess the only other reason not to pick Iksar would be the XP penalty but what is the rush in leveling? Want to be better and level a bit slower or be worse and hurry up to a largely stagnant end-game that isn't going anywhere anyway? When you get to end game a bit faster and then there is no new content
ever are you going to really be glad you got there a bit faster? I doubt it.