Well, you can get the 9950 for £110 from eBuyer or the 6400+ for £92. The Phenom is 2.2GHz whilst the 6400+ is 3.2. At the moment I would say you'd be better off getting the 6400+ if you want performance, but make sure that your motherboard is AM2+ compatible for some degree of futureproofing. If more applications were to use more than a single core, and there were those available that could make use of all four of the Phenom's, then I'd say that the Phenom would be a much more viable option because there would be some advantages to having more cores versus less cores with a higher clock speed.
The only reason I bought the 9950 BE is because I want to be using a quad-core CPU now ready for when applications do start using multiple cores more and more. I have no plans to sell my dual-core rig (might upgrade the CPU from the 5600+ though) any time soon because it's a good piece of kit and with a slightly better CPU in it would be able to keep up with the latest games. It can already run Crysis quite well with all the settings on High, which would do me just fine, to be honest. It is probably going to end up replacing the cheap Dell of my mother's, though, because that thing is slow and my brother is quite a gamer, but he's held back by only a 2.0GHz 3000+, slow RAM and no dedicated graphics.
So, it's not yet solely a budget-thing. Realistically, I think that a lot of people would want to wait for quads with a higher clock speed (although I appreciate that overclockers won't have to endure that because they can fiddle and gain extra performance from the 2.4 and 2.6 processors that are available at the moment) before making the jump.