If we compare a late generation K7 like Barton with a later generation Netburst, we can see that for PIII level code they are about equal. I base that off of SANDRA's marks for both processors, and is the reason why I stand that Athlons are optimal for older gaming, all the way up to the DX8/9 era. This paradigm does change however, if you have code that is being optimized for longer pipelines, streaming extensions like SSE2, and in a big way, memory bandwidth. That last point becomes a big deal as graphic complexity increases. I was looking at a review where they compared 3200+ with the first 800mhz bus P4, a 3.0ghz northwood. They basically trade blows, but if you factor in non-gaming tasks the P4 looks superior. Now figure that you can get a factory P4 at 3.8, and that getting a Barton to 2.6ghz is a task requiring some skill and luck; clearly the P4 is the easiest to obtain. Granted, the 3.8 specimen is actually a Cedar Bridge; basically a Prescott with a die shrink with lager cache. But it isn't overclocked, so allowing this constraint I would believe that the P4 would ultimately be the performance leader, since you have the a memory bandwidth when you need it and the raw clock speed will pull it up even in legacy applications. It is worth noting that particular processor uses socket 775, so one will end up with PCI-E graphics unless a few certain motherboards are used.
That being said, I still personally use an Athlon since they work just as well for most stuff and use a lot less energy.
Athlon XP-M 2200+ // Epox 8KTA3
Radeon 9800xt // Voodoo2 SLI
Diamond MX300 // SB AWE64 Gold