I have an iPod touch 4th gen which came out not last year(they only added the white faceplate) but the year before and while I have some annoyances with email overall performance is better than I expected for a single core device. It runs as zippy as before, except for the app store is a bit problematic, but I have heard of others having issues with that. Personally I would look up the features you'll get for the iPhone 4 and see if you want the update based on the features. But I don't think you will end up with a near broken phone if you update to iOS 6, so if you want I say go for it.