If you are going to use 3" pipes, you should really upgrade to maybe a Q45 or other 3" Throttle body as well. Or again, you will lose all the benefits of the big 3" piping and intercooler. The parts really need to work as a system. 2.5' would have been fine, as long as the whole system was 2.5". You basically don't want to have any transitions in the system, and if you do, you want them all to be from smaller to larger, not larger to smaller. It's not to say it won't work, and you could use the smaller TB temporarily, but you would eventually want to even out the diameters if you want your intake system to be functioning optimally.
If you want to know the whys and wherefores look up posts by RickyB on mr2oc about intercooler piping.
BTW, I'll buy your RC throttle body. :smokes:
J.