is there much difference in the hyper 7 than the hyper 8? would i be better off spending a little extra and getting the hyper 8 than the hyper 7?
im talking about the pro kits

Both are good buggies but of coarse the 8 is the newest version. If you are going to race then I recommend getting the 8.

I have a Hyper 7 and like it a lot. If I were in the market for a new buggy, I would go for the Hyper 8.

Yeah I love my hyper 7, but the 8 is great too. As long as you haven't got cash flow probs go for the 8.
If however you're worried about cash the hyper 7 pro is still a great buggy.

Just our of curiosity...what are the major difference? Are some of the parts still interchangebale????

Only some parts. Diffs, knuckles and a few other bits and bobs.
It was designed from the ground up a new buggy though so its not an upgrade that can be done to a hyper 7.