What would be the best choice between an INTEL CORE I5-4430 3.00GHZ 4-CORE (LGA 1150) and an AMD FX-8350 4.0GHZ 8-CORE (Socket AM3+)?
If you're using the rig in your specs, just get yourself a 3570k/3770k, you can probably find them pretty cheap now. Makes much more sense than what you're planning, especially since you could do with a PSU upgrade depending on the GPU you end up going for.
Actually a 3770k or a 3570k and a fast gpu will cost more, but I will see if I can find one of these CPUs.
I really doubt it'd cost more than what is being suggested, regardless of where you are in the world. There's something like a £30 difference between a 3570K and a I5-4430 in the UK, and while the 4430 is cheaper you'd need to buy a new motherboard. The 3570K will pop right into your current Z77.
That is a big problem with Intel CPU's. On the market they don't really depreciate in value. Even so, the 3770k is like $330, and the 4430 is like 200, +150~ for motherboard. So it's at least the same price in the end.