The world is your oyster as far as tuning goes, I think Devilsyam had one making about 170bhp.
TTs do a big bore kit (1050 IIRC), you can get the head gas flowed and skimmed, re-profiled or new cams, slotted cam wheels, flat side carbs, Nos etc etc.
A lightly tuned engine (135-140 bhp) can tie the standard chassis in knots if used really hard.
I would say upgrading your suspension and brakes (maybe some carbon wheels) plus the usual Ivans / pipe set up is the best compromise for road use, and thats why so many on the forum have similar setups.