Guys, you are making out as though he is going to see some godly difference with one over the other.
Because all he is doing is number crunching, which is what CPUs do best, it doesn't matter, it isn't strenuous work, just alot of it, so I would say more cores is better.
However, as 87dtna said, with the i7, Windows will see 8 cores rather than 4, because of 2 threads per core, and that may be the better option.
Both the 1090T and the 920 will handle what you want to do fine, just find out which is the cheaper option (for the board, CPU and memory) and go for that, because you will not notice any difference at all, but will save yourself a bit of money