Lucky,
What OS will you be running? 8.6, 9.x, or 10 (OSX) ?
I've found the GUI under OS 9 (all seem to be about the same 9.0.4 through 9.2.2) to be fastest so far on my Mac at work. The G3 233 I was running got 26hr times under 8.6 and 10, but 24hrs under 9.2. The system has been upgraded to 333mhz in the last few weeks, which dropped times under 9.2 to about 18 hrs.
I just tried switching over to OSX full time this week (dual boot) because some new software we will be using in the fall will require it. I found the CLI, which was not out when I last tried SETI under OSX. Under 10.0.3, I was getting 22hr WUs from the CLI at 333mhz. I upgraded to 10.1.5 today and expect a drop in my times based just on the way they improved performance in everyting else with this patch. I'll let you know how it goes.
If you got this computer just to run a DC project, I'd look for something else to run. They're pretty good at RC5 as I remember.