B20VTI

Im running a Full race top mount at the mo with a 3'' downpipe through to a thermal exhaust (no cat, no resinator).

got me thinking today of the advantages of a 4'' downpipe, has anyone on here got the following setup or would i notice no advantage over a straight foward 3'' -

- 3'' flange onto the turbo, straight into a 4'' downpipe, all the way down to another (reducer) from 4'' back into 3'' to then joining onto the thermal.

Would this be pointless???why??
Any advantages??

Im thinking it would be pointless, ive got a steel fabricating shop right nxt to me, spoke to them and they said it would be a piece of cake to make. Shall i do it?? yes/no?