Probably depends where in the country you live and how far your prepared to travel.
for power range of around 500/600
Collins Performance big turbo kit
Sabre Big Turbo kit
DEVIL Developments & MSD Big Turbo kit
Then you’ll need to think do I want methanol at some point.
I took the plunge and went with Devils about 550 mile round trip.. They will also fit kit you supply if you can get it cheaper than they can provide it. For example: I managed to get an NX2 turbo delivered door to door tax paid for £1600 and they had no issue fitting it
RS Edition.
FPM375 Rocks
The rest of the “M” maps suck