Im planning to build a computer and i was wondering what to get hd4870 or HD 4890?

hi everyone i'm having a computer built in a couple of days and leading up to the countdown im sarting to wonder should i get the ATI hd4870 or the HD 4890 im playing on a 22inch hd screen. The price difference is about about 25 pounds which could be used for something else like a gaming mouse bigger hd etc so tell if you think the 4890 is worth REALLY the 25 quid more price tag cos i'm pulling my hair out here lol thanks a bunch