I use Momentum. I think it is 1 Ron more than V-Power or is it BP Super, can't recall but every Ron helps. I consol myself with the thought I am buying 5* fule at 4* prices compared to BP, Esso or Shell.
I think Mike from Bamford said the premium fuels are worth no more than 5BHP.
Use higher octane fuels such as BP, as they apparently contain less ethanol which screws up the old fuel lines and my fuel pumps (especially when used infrequently)
No knock sensors on an old Vanquish, so no power difference.