Macbook Pro 13" i5 vs i7

I could use some advice. I have an old macbook pro (15") and 23 inch LCD. I dont need the 15" model for Aperture work because I use the LCD.

I do however need a new laptop as my 2008 macbook pro is starting to become sluggish and I notice a lag when using certain Aperture editing functions and I can hear the fans going as well.

So I'm just wondering if there is much of a practical difference that I would actually notice between the i5 and i7 models because if there is no real world difference, then I could save money by getting the i5. I like the 13" over the 15" model for its lighter weight/portability and I dont mind the glossy screen because my LCD is the anti-glare version.

I should add that I rarely use the laptop for games, certainly not 3d or graphics intensive games. More like chess and bridge.

Thanks for your help.