The i5 will perform better and likely last you longer.
PileDriver will probably be about 10% more powerful than AMD's current Phenom II / FX CPUs. That will make PileDriver about equal to the 1st generation Core i3/i5/i7 CPUs.
PileDriver will need to be about 28% more powerful than Phenom II / FX to be equal to an Ivy Bridge CPU.
First off, kudos on the avatar. Dave Lombardo taught me how to play drums. South of Heaven is still one of my alltime favorite albums.
From the looks of it, Piledriver (Vishera) is going to be 15% faster than Bulldozer and close to 20% is a slight possibility. At that range, if they come out with some competitive pricing and not the $300 tag the 8150 released with, it would be a very viable alternative if the 3570K is still $230-240.