If you don't want to spend HUGE sums of money - the best (and probably not that expensive a way) is to get to somebody with a Dyno who KNOWS Rockets and let them get the best possible out of the stock setup.
The biggest bottlenecks are the exhausts - especially the stock headers and the intake.
The best intake solution currently that will fit under the chrome bearclaw is probably the RAMAIR.
http://ramair-filters.co.uk/triumph-rocket-iii-filter-kit/triumph-rocket-iii-filter-kit.html
There are more radical intake solutions but some CAN be noisy.
Exhausts - it all depends how much you want to spend vs how much you'll get out of it.
For example there is not much point in getting a system that aids breathing at 6000rpms if you'll only be pushing it to 5000.
As Art says - 165-170hp is fairly easy.
The DoBeck and Powercommander-V units make home tuning easier - but an expert and a dyno will be better.