With your current mods you can get a stage 1 remap, 230-240bhp
If you got a downpipe you could get a stage 2 map which is 250-275
If you got a downpipe and hpfp you could get a stage 2+ map and your looking upto 280ish
a cat back isnt needed for a remap.
I have assumed you have a gti ko3 and not a edition 30 ko4.