3" Downpipe

Hi I just went to a muffler shop and put a new 3"hi-flow cat, 3" exhaust and a 3" Dyonomax Muffler on my GSX 99. Now I would like to know if I should put a Downpipe on my car ? I have a T-25 but I will upgrade it to a T-28 in a few weeks. I would like to know if any 3"downpipe for GSX 99 fit bolt on on my car. I also want to know how much inches is the exit of my t-25, can I bolt a 3" downpipe to my t-25 ?

Most 3'' downpipes are 2.5 before the flex section. I know the apexi and RRE ones are like this. There is no need for 3'' to the turbo unless you have a large turbo and tubular o2 housing.

the wonderfull, fantastic, well built 3in megan racing downpipes on Ebay are $110 shipped.