Just now I'm using a 2200 and a 3800 and, really, in use the difference is not noticeable. Indeed an old 750 is as quick for most things. A lot of imaging work shows it up a bit but that's the only thing.
When it comes to speed I honestly believe there is a lot of hype to get us to buy the latest most expensive bit of kit. Having said that though it all depends on an individual's disposable income I think. E.g if £60 represents 5% of of weekly disposable income then I'd probably go for it but if £60 represented 20% then I wouldn't.