You will be fine running 2.5" from downpipe and probably wont notice any draw backs if you aiming to run circa 200 bhp When chasing bigger numbers and wanting best possible performance downsizing is not the best thing to do
Never said reducing the turbo exit Usually they are kind of small I have a 2.25" turbo exit, and I did a 3" downpipe with a cone, and after the downpipe, set it to 2.5" (nightmare to get a 3" over a mk2 rear axel)
