The only portions of CATIA that are multi-threaded are DMU Navigator (the CGR Tesselation process) and FEA. Of course, if your data is coming from LCA/VPM, the multi-threaded feature doesn't work.
One thing to watch for - CATIA tends to send the same tesselation job to each of the processors. We've seen this on an 8 processor Onyx, where it takes longer to load an assembly than it does with the muli-processors turned off.