Referring to my (much) earlier post, why not look at diesel? Insurers haven't quite yet caught up with the fact that they go extremely well now and as such offer good premiums anyway.
They're also easily tuned via the diagnostic port and can give very impressive torque, power and performance gains for a little over three hundred quid.
THIS IS VERY IMPORTANT!!!!!!!!
You MUST advise your insurer of anything you do to change your car's performance.
Most [insurers] struggle to understand the remapping process and generally apply a 'chip-tune' levy of thirty or forty quid at worst. They will explain this to you when you have the telephone conversation with them after your car has been tuned, or remapped.
The 'phone conversation will quite likely be recorded by the insurance company. They [your insurer] will provide you with a revised Policy Schedule and possibly also with a new Certificate of Motor Insurance.
If there's ever any future dispute as to the validity of your insurance then you can refer to the recording of the phone conversation. Under the terms of the freedom of information act 2005 (and subsequent revisions thereto) your insurer has an obligation to provide you with that recording.
In short, so long as you declare everything, your insurer will have no means whatsoever to wriggle out of meeting a claim made by you, or, indeed, a claim made against you.