....
Why seek such big power on a FWD car when you'll also be potentially stressing everything else unless you spend serious money on internals etc?
Either trade in for an Ed30 or 'do a jonnyc' and strip the car etc.
Even VWRacing's K04'd GTI 'only' pushes out about 330 bhp and is hugely helped by its Quaife and suspension, brakes etc. Get a Quaife diff!
You need driveability - All year round - You live in the UK!