Gotta agree, Optimax is the nuts.
Always used to run my company cars on Superplus (pre Optimax) because a) I wasn't paying the bills, b) it made more car more economical (believe it or not) and c) the engine always felt more responsive and powerful.
When I bought my own car (V6 SRi Vectra) I ran it almost exclusively on Optimax, which had just been launched at that time. On the half a dozen or so occassions I got caught out and had to fill up somewhere other than a Shell, the car never feel as electric as it did when running on Optmax.
There is a definite performance boost, the car feels much more responsive, and I have always found a 2-3 mpg increase in economy over a tankful.
My old man has to use it in his Supercharged Holden, as anything else causes it to detonate like fcuk. If you're planning on running major boost, this may also be a factor to consider.
Now I drive an oil burner this is no longer an issue for me, but should I stray back to a petrol powered motor, I will definitely use Optimax, exclusively if possible.