I replied to a similar thread on PH recently, as follows:
Personally id try and identify what youre actually looking for out of the car. Getting power from these motors is a very expensive game in my opinion and if i were to start with a base car id probably look to spend my money elsewhere such as the chassis, tyres or tuition. They will give you so much more than just an extra 30bhp. My R has the following power upgrades: EVOMS Intake IPD Plenum GT3 Throttle body Fabspeed race headers with 200 cell cats. Full Remus Ti exhaust MASE Engineering mapping. Makes anything from 345bhp to 375bhp depending on whos rollers its on, make of that what you will. That to me is a huge amount of outlay to gain very little over the standard car. Spend your money on some RSS Tarmac lower arms and some decent geometry setup aka Centre Gravity. You'll enjoy the most amazing steering and turn-in. Genuine improvements you can enjoy all the time and at all speeds.
Not trying to pee on your chips mate, just want you to have realistic ideas for gains vs monies spent. I think you would be seriously lucky to see 15bhp from just a map. Reliastically more like 5bhp as a headline figure is probably more like it. Yet you may pick up some mid range torque here and there and maybe some improved drivability. Alternatively, throw £300 quid at a track day and you'll see just how impressive your Cayman is in standard guise. You'll have more fun in a day than an extra 5bhp will provide all year and memories that last a lifetime. Start adding some tuition to that and you'll improve the one component you'll take into every car you'll ever own/drive again