Originally posted here by Tim_axe
From what I've seen, all of Intel's recent (Pentium3 on up) processors have a full-speed L2 cache. Even their Celerons. I think half-speed L2 Cache ended with the Pentium II era. Feel free to correct me on this for Intel's Desktop offerings. ( Processor Specs @ Intel: http://processorfinder.intel.com/scripts/default.asp )
That may be the case, but I seem to remember some issue related to hyperthreading that would increase cache latency and slow down cache access. I also wouldn't put a whole tonne of faith in a document that simply lists the cache speed as identical to the core clock listing (for a P4 2.40A, "2.40A GHz").

I'd love to get my hands on a dual Opteron board with AGP 8X support, unfortunately it puts the systems well outside of my price range.