I have 800Mhz G4 without L3 cache. An MDD with 1.25Ghz that probably is overclockable without to much hassle will be significantly faster I think not ? Well I only take it if it's really cheap, else will buy myself one of these:

http://www.newertech.com/products/maxpower47.php

they are not very expensive and NEW. If I see some of the prices on Ebay for a comparable second hand Sonnet upgrade ... not too bad I think.