Would overclocking my 9600GT give any noticable performance increase? Right now I am playing Fallout 3 on Ultra High settings and some AA + AF and I notice lagging at times.
Those reviews aren't actually reviewing the 260 and the 4870, but they are included in the benches. I always try to find the latest reviews so that we can see the performance from the latest drivers rather than at the card's release 10 months ago.
I have a GTX 260 (XFX GeForce GTX 260 XXX Edition to be exact ) and I would highly recommend it, it is way better than my old 8800GTS 512MB ( which is faster than a 9600GT) so I reckon you would notice the difference. I have a 22 Inch screen so I was in a similar situation to you. I went for the GTX at the time as the XXX Edition was on offer and was cheaper than a standard 4870. Plus you get PhysX with the GTX and if you are comparing it to the standard 4870 it has more memory. So my vote goes to the GTX 260!
I also voted for the GTX 260. If performance is similar between the two cards, then I would most defiantly go with Nvidia. I find their drivers to be much better than ATi's drivers. Plus I hate the catalyst program. I think Nvidia does a much better job with their software.