I think Optimax can give an initial feeling of more oomph on an older car because it helps clean the fuel system and cylinder head out. Using it on a new low mileage car would probably not make much difference.
I tried it for a few months on my 145QV and to be honest, decided it wasn't worth the extra cash.
Well I did 150,000 Km's is a 1995 SEAT Ibiza Gti 2.0(second car) using Optimax. Car still ran like a new car when I sold it at 160,000kms. Used Castrol 10W60 oil as well. Dealer was most impressed with it.
The only engine problems I had was a new coil and distributor. Fuel system was still original at time of sale.
Car returned a consistent 32 mpg average over its life (mostly city driving).
I also use this fuel in my current Alfa 147.
From my experience this fuel does seem to keep the fuel system and upper engine in good condition.
NB SEAT engine did not use any oil even after 160,000kms-7500km oil change interval