i5 since almost no games on the market nor in the foreseeable future is making efficient use of more than two cores so it is unlikely that many games will make effective use of a 4C8T CPU within Ivy Bridge's mainstream life.
It took nearly 10 years for programmers to get used to program for dual-core PCs, I would not be too surprised if it took another 10 years for them to get comfortable scaling beyond quad-core. Every time you increase concurrency within code, you increase the number of possible bad interactions between threads with associated hard/impossible to reproduce bugs.