Travel to Hinkley for an R-Tech map. It really will be worth it.
What he said.
I have the same mods as you with only the addition of a BCS cat back, i made 268bhp/334lbft with a stage 1 R-TECH map.  The drive from bristol and back was worth it. 
I would imagine that mine would make similar power too but I worry that much torque would quickly destroy a standard clutch :(
Lot's of people do have issues with slipping on standard clutch i think.  Mines fine with it, plus, are you really going to be using all that power very often?
R-TECH will make you sign a wavier about the clutch btw.  They say it will take about 20% life off the clutch, but hey, this is the downside of modding a car eh.