I haven't seen any publications that compared and tested both the 3i vs. the 3s. Considering there can be variations between tests it hard to compare one vs. another. For example, for a 3s 5dr there was a 0.6 second difference between C & D test results vs. R & T for 0-60 times. There's a lot less info about the 3i out there too. I'm going to guess that a head to head comparison would put the "s" about half a second faster from 0-60 and probably a bit more than that for the 1/4 mile. What I'd suggest doing is going to a dealership that has both and see how each feels yourself. Make sure you go out w/out the salespeople so you don't have them distracting you.
Is it worth the extra money?
Depends on what options you want. The difference in price isn't that big if you want power options and AC. Once you add to the 3i the $1400 power package (consists of options all standard on the 3s) and the $275 fog lights (also standard on the 3s) the difference in invoice is just $581. So I think it comes down to how much you want those things. For myself, I really wanted the AC, power options and cruise control so it really didn't look like I would save very much with the 3i. Other things to factor in if money is really tight for you are gas mileage and insurance. You'll get slightly better mileage with the 3i. I doubt there is a noticeable difference in insurance but I really don't know. It's not hard to call for a quote to check though.
