I agree - unless the driver was really crap, a Typhoon I was lapping with at Wakefield couldn't get away from my mildly edited '04 XR6T... braking gained him maybe a couple seconds per lap, but no way could I believe 10sec.
I have a 2004 5-speed, with a minor edit done by MRT (only 7psi) and I haven't had a problem? All the niggles I've had have been with stupid things - Horn not working, interior lights not working etc etc.