Bridgestone Turanza are a good tyre though bit pricey for an 18in -20in wheel.. I got 120,000kms out of a set on 17in back when i had my vr commodore. Atm im running Kumoh's 18in and they seen to be wearing ok so far only done 20,000kms on them
In my 06 Omega i use to get 10-12L/100km now im getting 14-15L/100km regardless if its city or freeway driving and i get 450-500km. My wifes Vy gets better economy than i do now @ 11-12L/100km and it gets 600-700km per tank. Both run on Premium Unleaded.