different opterons on same mobo

am trying to put together a dual opteron with sli.
do the opterons need to be the same. i have 2 252's and a 875.
could i use the 875 with one 252?
if not would a 275 work with the 875.
secondly with the graphics card,
i have the ibm t221 (dg3) with a Quadro FX 3000, at highest res of 3840 by 2400 it takes 3 seconds to open 5000 by 3000 image.
the file size is 45mb.
would the opterons speed up the opening time enough to make quadro sli a waste of money. was thinking of two Quadro FX 3400's.
was going to use the supermicro H8DCE mobo
thanks
sean

i doubt you could combine single and dual core cpus in the same system - but you can use other opterons as lowest-common-denominator (e.g. an 875 and 865, or 265 and 865)