Hey Vanquish,
In terms of running the "classic" OS (meaning anything other than X), you won't see any real performance gains from the MP machine (with the exception of programs specifically written to take advantage of MP's... ie Photoshop and a couple of others). Within OSX, there is system level support for OSX, HOWEVER, in order to install X on one of these machines, you would need a G3 or G4 upgrade card. So to answer your question, IMHO, I would go with the 9600/350 if I was running general applications, the 9600MP if I was going to use it for MP enabled programs, but you might also consider buying a low end iMac or other G3, depending on your needs/budget, because they can be had pretty inexpensively now-a-days.
That being said, I'm not too familiar with Linux and how the variants are written for PPC, so you might want to post your question in the <a href="http://forums.macnn.com/cgi-bin/ultimatebb.cgi?ubb=forum;f=28" target="_blank">Linux on Mac Forum</a> . You also might want to investigate Yellow Dog Linux.
The 9600 series had 10BT...
good luck!
dave