According to Andrew (volkswizard) the TCR has more bhp per tonne than the R. He did a video of 10 reasons why the TCR is better than an R. The other thing is insurance costs on the R due to a load being stolen. I don't fancy being one of the statistics.
Sounds like you've already made your mind up Chris - better get that TCR ordered before the books close on it.
Not sure if insurance will be an issue with the R - I don't recall scores of Rs being stolen in Tyne and Wear. My R cost me £10 a year less than my GTD and the premiums didn't go up significantly in the subsequent years I had it.
I'm sure Volkswizard could come up with 10 reasons to get an R over a TCR (most based on practical real world use rather than ideal track conditions). Both will be good cars, they're 2 sides of the same coin.
I think your biggest issue with either will be whether you'll come to like DSG or just have to live with it - like me, I'd so much rather be in a manual, if VW hadn't taken that choice away.