I wouldnt bother with the cat back just yet. When i fitted my 3" Downpipe (whilst retaining the standard cat back) it made a much meatier sound as well as providing the extra oomph and the possibility of using a stage 2 map.
Miltek cat backs are circa £500, stage 1 Revo remap is £500. So a grand for 40hp/60Ibft gain.
or
get a pipewerx 3" Downpipe £450 and skip the stage 1 remap and get a revo stage 2 remap £550 and get a 50-60Hp/90Ibft gain for £1000.
plus you'll still get a meatier sound from the exhaust, I never had my cat back fitted unil after i had my HPFP and Stage 2+ installed.
you could even get the same perfomance gain with a cheaper remap £399 will get you the stage 2 shark perfomance which made neigh on the same figures on JKMs dyno as the REVO stage 2 cars do. 260hp/290Ibft, taking into account you have the standard intake and cat back, you would still be looking at 25-255hp for a total price of £850
not that im trying to tempt you to get more power, lol. but id def skip the stage 1 route and go straight to stage 2
or are you stage 1 already??