A couple of years ago the factory were trialing a supercharger in the Mk 11 Roadster. This forum reported that during testing at a venue in the USA it failed in some way. So the supercharger option sounds like it could have reliability issues for the 3 litre engines.
About the same time Richard Thorne dealership were offering a power upgrade on the Mk 1 Roadster, involved manifold work, cams, ECU etc. I discussed it with them and the cost was 3K plus VAT and fitting for about 275 Bhp. They have just sold a grey Roadster with this option fitted. Might be worth a call to see if the modification is still available.
I have a Mk 1 with the bluefin fitted and sports exhaust but the difference is slight and as you say probably all at the top end.
