Mass will have a small impact too, the lower mass the better. But as said above, the Optimised Mass is the key stat. Can get up to the low 50s % improvement; including the secondary effect.
The perfect key rolls is 50% increase. 5% bonus optimal multi, 5% more fuel per jump. I've seen all of these- just not exactly together. My Anaconda has a perfect 50% roll and IIRC 3% more fuel, but no other bonuses.
Is the "more fuel per jump" a separate secondary effect?
I had one roll of 49% plus 4% secondary which I was delighted with. Pity it was only on my FAS, I'd love to get that roll on the Asp.
Is the "more fuel per jump" a separate secondary effect?
FAS and ASP share the same fsd module, swop it when you need ti change ship.