The highest intel CPU that it will support is the intel Pentium 233MMX. However, depending on which model you have you might be able to overclock that all the way to 300MHz(or more).
As for AMD CPUs, I'm not sure, but if the Asus P55T2P4 supports the K6-2+ 500MHz, then there's a high chance that a TX motherboard will too.
As for Cyrix/Centuar/IDT/Rise/etc CPUs, I have no clue, but you shouldn't even be bothering with those.
As for cacheability(is that even a word?) the TX chipset only caches 64MB of your main memory, and is non upgradeable. The HX chipset also caches 64MB by default, but this is upgradeable to a 512MB cacheable limit via a TAG SRAM upgrade.