How much of a difference will changing the charge piping from the intercooler to throttle body make? right now I have 2", and part of it comes off of an MKIII supra, and that too is 2". Likewise, how much of a difference will it make from changing from a 2.25" downpipe to say a 2.75? thanks guys

 

There will be all different kinds of opinions on the charge pipe sizing so here's mine...unless you're boosting the hell out of the thing (which it certainly doesn't sound like) 2 inches is fine. You just have to take into account air velocity and flow rates when choosing pipe size.

As far as enlarging the downpipe. Yes that is a good idea, less exhaust restriction makes your turbo happier. Make sure it's heading into a nice free flowing exhaust.