I am currently running a Komo-tec phase 3 power conversion on a 2006 Exige Cup240. All pulleys, gearings, rods, pistions, etc. remained stock. Dyno runs on a MATA rolling road on a hot summer day (90 degrees and high humidity) using a custom built piper catback exhaust provided 292 hp at the crank (ca. 230 WHP) and 245 Nm of torque. This is good for 0-62 runs of about 4.3 secs.
With cooler Fall weather coming and less humidity, 305 hp should be possible. Due to the supercharger architecture, however, I don't expect any more torque to come out of this setup. The torque with the phase 3 is much more even than the phase 2 and really pulls nicely out of hairpin turns
Biggest obstacle to really tearing up the asphalt is - as always - the too-long gearing and the transmission itself, which has a power limit of about 300 hp. If you are serious about tracking the car, I would consider putting in the fantastic unit originally designed for the Toyot MR-2 turbo which is good for at least 550 - 600 BHP
Additionally, Jubu Racing in Austria makes straight-toothed forged gears which are MUCH more durable than the stock unit.
I also installed an autonomous oil cooler for the transmission with heat exchanger. This might just save your mechanicals....
All in all, the Komo-tec power packages are pretty reliable and deliver good value IMHO. Since that much power is just rediculous on public roads, you should first consider the kind of driving you'll primarily be using the car for.
Good luck with all the options!