Will I regret updating my 4 to iOS7?

When I bought the 5s I elected to keep my old iPhone 4. The guys at the store told me iOS 7 would "slow it down." So I've left it where it is (6.1.3) but am itchy to try the update.

Thing is, I'm still running my beloved Power Mac G5, which is stuck at iTunes 10.6.3. Yeah, I'll get something Intel eventually. Meanwhile though, if I bring the iPhone 4 up to iOS7 I guess that means it won't be able to sync with the computer because iOS7 won't play with such an old version of iTunes. Correct?