Starting using Optimax but now only use Ultimate cos I read somewhere, not sure whether it was this forum or another one, that Optimax is only 95, and they put some sort of additives in it to bring it up to 98...
Knowing my luck it is probably an urban myth, but must admit I get better mileage and performance outta the Ultimate....
BTW - lots of people here in Canberra call Optimax 'Crappymax'
:-)