Well the simple fact is....My x800pro is unlocked to have 16 pipelines enabled...., I also happen to keep it at 520mhz core and 1100mhz memory. Stock it is 475mhz core, 900mhz memory...Biggg jump. The point was that, even on an older rig like mine every mhz counts towards better performance. If I bump it up to 525mhz core and 1150memory I get smoother framerates, and i've got fraps to prove it.
I've done various testing over and over with fraps and games like oblivion, fear, CS:S..etc.. That little extra 10mhz here and there does equal out to another few fps here and there. If I wanted to I could keep my x800pro @ 535mhz and 1200mhz memory all day and all night and I would see a difference via fraps.
Also, please realize that the x1650xt is not much better than the videocard i'm using now...not by much that is. Another thing to keep in mind is that my cpu is extremely limited since my mobo is only limited to single channel support. We all know how much p4's love bandwidth, and without dual channel, it just kills it for me.
The x800pro is bottlenecked in my system....just like the x1650pro would be in his...just like the 7800gs would be in mine as well. But that was not the point. The point is that even with the bottleneck I can guarantee you that there would be a difference between a 7800gs and x1650pro in performance, even with the 2.4ghz p4.