Weight will only be about 50kg difference... 60bhp more and AWD. Not to mention a 0-60 5.5sec compared to 7.1 sec 
50 Kg? We'll see...I'd bank on nearer 100 Kg.
60 BHP...I think not. 50 and a bit maybe...at the crank, according to VWs figures. (210 PS vs 265 PS)
You do know Haldex has losses?...around 80 BHP total on a TT/S3/R32...compared to 50 for a FWD...so that's a grand total of 20...being generous, 25 BHP more...with nearly 100 Kg more to lug about.
Your 0-60 argument doesn't need explained...nobody has argued that off the line, a 4WD car won't be considerably faster under most conditions...but once out of 2nd - at about 60 MPH, it becomes irrelevant...and the extra drag and weight counts.
How many times have you seen Mk5 GTIs turn in slower 0-60 times but faster 1/4 mile times? Power to weight counts once rolling...and a standard Mk6 GTI won't be too far off a Mk6 R once you get it into the top of 2nd/3rd.
Seriously, in skilled hands, the GTI isn't far behind out of the box. Nobody is saying it's not slower...but it sure as hell doubt it's 10% slower once you get off the line...which means in normal driving, it'll be pretty close....as it is in the Mk5.
Give me the Golf R and i will leave any GTI well behind straight or twistys anyday of the week 
Catch you at GTI International one year...and we'll see!
If you can't take 10% of time off me, your argument has failed and you buy the beers.
Just don't brake too hard...ot I'll hit the back of you...I'll be that close!

Anyone wanting the quickest and most tunable Golf yet.... the Golf R is the one to go for imo.
No argument there...