If you change 0.48 to 0.63 ex housing you will get better ex flow and increase power but lag too.Lower compression will reduce engine response.If you are Std compression that means you have a chip mapped for std compression.The best way to minimize lag is to fit a Ball bearing Turbo you can go bigger turbo will the same or ever less lag than your T34.Ball Bearing turbos spin very fast.See them at www.turboneticsinc.com
I used a TS04 on stage 4 cossie low comp 4x403 with almost T34 lag and a 3 door
with 60-1/T3 Hi-fi with the same lag as a std T3 with impressive power .


Roger