awalleye, a 980x with 580's would be better. Basically, the formula is this for detirmining class:
# of cpu threads + # of gpu cores + cooling type (the handicap are listed in the rules for types) = total #, which tells you what class.
So for gpus at least, you want to use the most powerful ones you can, as 1 580 counts the same as 1 450, 2 580s=2 450s etc. So a 980x with a gtx580 would be the same class as a 980x with a gts450.
I can try and explain it more/give multiple examples if it is still confusing to you.
EDIT: oh yeah, also, you are allowed unlimited downgrades. Here is an example. You sign up with a 980x, 1 580, and dice (just an example remember). That would be 12(threads)+1(gpu)+3(dice)= 16. That would be class A. That means you are permanently in class A. But, if say dice fails for you, you can go to air cooling, but you are still in class A, even though with air your handicap total would be less. Or if your 980x died, and you used a 920, same thing; you would stay in class A. Basically, once the event goes live, you are in your designated class, but if something goes wrong, you can replace it with lesser parts, but stay in that class.
I think you can change up your config until the wars start, you would just have to update where you signed up.