I have overclocked a lot of Macs. The very first time is scary, but the next ones is just a mater of being very carefull.

I have done a lot of speed test between them. Acording to my results, a 166 Mhz system bus is prefered over a L3 + L2 combination. I think you will note linear speed increase over 1.666 Mhz (if where posible in this machine). 256k of L2 is enough for a 166 Mhz system bus, even in video encoding, (where low bus speed, despite CPU and cahes is very annoying).

Sorry for my bad english