Update,
Well it's certainly working - took .95 of a second out of my time at Curborough on Saturday posting a 30.18 on road tyres with the back stripped out. 5th place over all and fastest MKV currently on the C-GTI's historic table.
If I'd bothered with the R888s and putting the ARBs on hard, I may have been in the medals?!
To put that into some sort of comparison, I was less than a second behind a 460BHP (+NOS) stripped A3 quattro and some 200BHP 800kg MKI GTIs with LSDs and on sticky tyres. Fastest was a big turbo'd 16v MKII (VW Motorsport lightened shell) again with an LSD and stickys by just over a second.
To say I'm proud of that would be an understatement.