They certainly are different and the M05 with it's more balanced look appears as though it should be faster, but having used both back to back for some time at my club (Eastbourne) we've found the '03 to be quicker on the tarmac.
Quite why we don't know but the '05 just has moments of too much understeer, but dial in some steering and all it does is give it a large amount of oversteer.
Where as the M03 tends to be more sure whatever the surface, whatever the conditions, often with a near box standard setup.
Overtime everyone that had the M05 at Eastbourne have slowly gone back to their old cars
On carpet however it seems to be down to personal preference.
Read through the the pages of info on Mini.net and you will have yourself a fast car.
If you allowed to, run it with no extra weight and very little ride height. It makes a vast difference
