I have two windows PC's, one with an i7 3770 and the other with an i5 3550. I don't see any difference
with Sonar X2 on either machine, with Windows 8. There is a difference with the Intel video (different versions) and some other, non Sonar, functions. The i7 machine is my primary and the i5 is a "backup" system.
For the price difference I would go with the i7. My recomendation, when a client asks me about new PC's, is "buy as much as the pocketbook can stand" or "buy overkill".