The only Pentium 4's with a 800mhz frontbus have hyper-threading.
The type of chip to buy depends on the type of gamer you are...
If your looking for the best performance out there then I'd go with the p4 3.2 ghz special edition or the Athlon 64 FX-51.
If your looking for something that's maybe a less inexpensive but still runs extremely well, go with either the Pentium 4 3.0 ghz or the Athlon 3200+ XP.
Ok, this list could go on for a while so I'll break it down for you...Unless you are looking to speed up your computer to speeds you can't even notice the difference with, go with something around a 2.0ghz +. I personally recommend Intel.
Trebor: Not all above 2.66 ghz have a 800mhz FSB. Like I said above, only those with hyper-threading have a 800mhz FSB.
spfd: The Athlon 64 doesn't really support many applications or even an operating system, but people still buy it
Anyways, hope this helps you out