Basically on the Stormcloak side I get a huge FPS drop from my constant 60 to about 5. No idea what is causing it, none of the fighting has started yet it only happens when I get to the camp.
I've tried disabling and re-enabling all mods to no effect.

I have played the imperial side many times without a problem, the only difference between now and then is Dawnguard and me updating my nvidia drivers.

Going to try using the console to complete the quest to see if it happens to the other fort take overs.

Try turning down the grahpics setting during the battle

If his fps drops from 60 to 5 I don't think it has anything to do with the graphics settings. I have like 35-40 fps at all times, even during the battle.

I used the console to complete the quest... No repercussions so far, forts seem to work fine o.0. No idea what causes it.
It is most definitely not my graphic settings, already tried turning them down, I'm not talking lag here I mean can't actually move, it took me 5 minutes to run across the stormcloak camp.