I would talk to Abbey, think an aftermarket exhaust and y-pipe will compliment the re-map too (as well as the spacer), I wouldnt concentrate too much on what your bhp goes up to though, I want to get mine done for better throttle responce, cleaner gear changes and better fuel consumption... and obviously a bit more power , i'd be happy with around an extra 20-30bhp , if you believe what the manufactures say then I calculate that I will have an extra 40bhp from my mods and plus say 50 bhp from a remap , that will take my car to around 370bhp
I may have to advertise my 370bhp 350z on ebay for £15k when its done