Hi,
I have the GTT 260 conversion and while it seems quite fast im not completely sure it actually is if you know what I mean but this could well be to do with my engine being new when the work was carried out and may have opened up now therefore needing a remap which im going down to GTT for soon as at the minute my car only has 205bhp so something is wrong but Roland is going to take a look for me.
As for Dastek they are very good I assume you are talking about there main office in Fife? I will be fitting an M7 Air Gain System soon and have my car booked in with them to be looked at for anything that can be improved upon to make it faster

and will probably end up with a Unichip box fitted and tuned on there Dyno. I have used them before on my old car which was a 2.0 Ford Focus and I got that up to 180bhp n/a.
If you decide to use GTT obivously you need to speak with Roland but if you dare to be a bit different then give Dastek a go. The guy you need to speak to is Paul Wilkins on 0845 345 4045 I know that they are now starting to offer there own Cooper S Conversions and are continually working on there own Cooper S.
Hope this helps a little.
Jamie