That's a nice overclock...the most I could do on my old T-bred B was 2450MHz or so.
To be honest it's been ages since I've seen Athlon XP's (especially overclocked ones) included in any benchmarks, to know how exactly they compare to A64's (or Opterons, in this case). What kinds of things do you do on your computer that may be CPU-limited?
For what it's worth, I recently went from that XP at 2400MHz to an Opteron 170 (dual-core) that's now running at 2600MHz - I saw some noticeable improvements in games even though I'm running at the GPU-limited resolution of 1680x1050.