my vote goes to the p3xeon, but the gap depends on several conditions: the tbird's mainboard, and whether the benchmark uses sse instructions.
if the tbird is running on kt266a or even nforce2 boards with ddr ram, and the benchmark doesn't involve using sse, it would surely beat the p3-800 and come pretty close to the xeon.
on the other hand, if the tbird is running on kt133 or even sis730 boards with sdram, and the benchmark makes heavy use of sse, it would lose to the p3-800 and be smoked by the xeon.

I just learned today that the 2MB Xeons actually use on chip cache. Wow. I always assumed that the 1MB and 2MB variants used cartridge mounted cache, and that only the 256K Xeons had on-chip cache. Had no idea Intel was doing 2MB internal caches way back in 2000...dang! Anyone know if it's the same 8-way, 256-bit system that's found in Coppermine and Tualatin?

Anyway my vote goes to the Xeon.

imho xeon will win for most tasks, especially for modern or multimiedia apps, athlon may however get the upperhand with very small code;

The chance of the xeon being dual or quad cpu is HIGH. That under win 2k or xp is going to be amazing.