No practical difference between either one. PCI 3.0 has been benched, it doesn't really have a noticable difference between PCI 2.0. For gaming in terms of CPU performance, Ivy doesn't even manage a 1% improvement over Sandy. You can't really go wrong, but if you want to save $10-20 get the 2500K.
money is not issue here....does 3570k has any advantage over 2500k in term of future proofing the system.
I say no. But if money is not an issue, you may as well get the 3570K for the false sense of "future proofing". Some people it makes feel warm and fuzzy inside. The 3570K might not have an advantage for gaming, but it does have about 6% improvement on average for everything else. You have to break at least 10% to really be worth it IHMO. But meh.