depends on the boost level, size of turbo, ambient air temperature, speed, etc, etc. you might not get any benefit for 90% of the year, only more lag as the turbo will have to pressurise a larger inlet volume.

i would start with a 4x4 one, get an act or secs monitor and check it. 4x4 i/c 50 quid, rs500 type couple or 3 hundered quid. plus the rs500 type will have bigger pipework normally used with a t4 size inlet turbine so you might also need new hoses or adaptors if you're going to use a t3 only (330 max)