I just rebuilt my Windows desktop. I used i5-3570k, on a new Gigabyte Z77 motherboard. I added 16 GB of 1600MHz ram. Spent about $300. I couldn't be happier with Reason's performance in all aspects. You can save some money by not buying the i7 3770k, maybe up to $100.
As someone said, you will not take advantage of the i7's virtual cores in rendering your songs. On the flip side of my point above, you can find some sweet deals on processor and motherboard combos which may support your decision to get the i7. Checkout Microcenter if you have one in your area or their website. And I have no association with that company!
Most folks I know only get the i7 if they are doing video editing. Either way you go, you will not regret your decision.