That's a good question, I believe most of the generic PCMCIA CF card adapters conform to the older non-Cardbus standard, as I use the same adapters in older Powerbooks. I suspect a "cardbus-enabled" PCMCIA CF adapter adapter is a very rare beast.
Performance of said adapter + Adata 2GB "60X" CF card in my 2400c (with cardbus mod) is very good, but not dazzling. Booting and random seek times are very fast but general use (eg. copying, loading) is no faster than a good HD. I'm using a 5400RPM 40GB in my 2400c so generally just use this for everything and not CF, I'd be inclined to use a big HD in other Mac notebooks too.
Another thing to keep in mind is that if you use two Cardbus PCMCIA cards in a 2400c and attempt to start up, somethings things go a bit screwy.
JB