As your car has got a full exhaust system IMO get the custom remap.
I have got a Jabba custom remap on my mk3 and it has been faultless. 199.9bhp/309Nm on Jabba's rollers running 95 octane fuel and no other mods, but I haven't had this verified on other RR's yet.
Is that all? My wifes Ibiza did more than that on a generic remap.
Having an exhaust will do nothing but make more noise - it's not the bottleneck in the system.
A 'custom' map would be nothing but something to write in your signature