the programs both use a different rendering engine
and really depends on what you are rendering,
for each pixel you've got to do a lot of different calculations, which can't be done in random order, so maybe the waiting line for the commands is more efficient on one or other program, really difficult stuff those rendering programs.
if you want to buy a $$ workstation,
the best thing you can do, is just go to the shop, and do some rendering on both machines, to test them for yourself.
any decent shop that wants to sell you this stuff will let you try, we are talking about big $$ here right?
keep in mind that the clovertown the advantage has of 4 cores, this can be very important for video rendering and other multi-core apps; and the rendering software shall be improved for multicore environments i think?
don't know the price of both processors, so can't give you a price/performance overall