Octane should be around 100 for your Aristo.
I use Silkokene octane booster, available from Demon Tweeks
Optimax fuel is fine, in fact v.good with octane booster.
Lag is reduced greatly by having correct octane, incorrect octane e.g.95 for normal fuel, 97 for Super Unleaded, 98 for Optimax will give turbo lag and damage pistons at high revs.