40 TFSi is just a downtune version of the 45 TFSi. There are many remap companies that offer to increase to 250bhp.
My nephew owned a Golf R until moved to a BMW 140i. I sat in the Golf R and it was impressive with the 300BHP on 4WD.
The A5 will not get anything close to a Golf R. I have a 211 BHP A5 and its ok for daily use but its no hot hatch and it won't be even with a remap due to the weight of the car. If your A5 is not a Quattro that's another issue of putting down that power on road. The remap will make the daily drive fun...but not a Golf R
If you want similar performance as the Golf R you should really consider the 3.0 S5