[Question] Buying new hardware for UE4 and coming games. Your opinions?

I’m talking about both at the same time. What i’m trying to do is getting the best hardware which is relatively inexpensive on the same time. I would like to stick below 650$ if possible.

Why is a GTX 770 better on UE4 than a 760? Just because the 770 makes better performance in general, or is there any special reason?
Should i buy a card with 4 GB or are 2 GB comparable? i guess 4 GB are worth it, right?

Do you think an Intel Core i5 4670 4x 3.40 is the way to go? I’m wondering because it has less cores + GHz and is around 60$ more expensive than the FX-8320. Does it even so have an positive impact on performance?