i agree on the shell fuel, mine diffently runs smoother on that fuel, problem is im not allowed to fuel her up at shells cus "er in doors" wants her flippen tesco clubcard points,
What "brew" of super unleaded is at your local Tesco. I ask, because many Tesco sites are still using 97RON. The Tesco 99RON super unleaded (supplied by Greenergy.co.uk), was proven to give clear power gains over BP Ultimate super unleaded (97RON), and the then Shell Optimax (98RON).

Obviously, Optimax has been replaced by Shell V-Power, which is also 99RON, and so should give identical performance as the Tesco 99 brew.
I normally run my GTI and RS4 on either Tesco 99, or V-Power. Usually, V-Power in the GTI, and Tesco 99 in the RS4 - but I do swap around sometimes for a few tankfulls, and to be honest, can't really notice any difference. However, if I'm unable to get either Tesco or Shell, and have to resort to either BP Ultimate, or the Esso SU, I can notice a difference, in performance and "smoothness". In fact, BP Ultimate repeatedly actually causes a misfire in my RS4 -
