Those of you with a std engine tune on this thread, can you honestly tell me you can detect the difference in performance or smoothness with E5 or E0 99 Ron vs E10 95 Ron? Don't get me wrong, I prefer to fill up with TM99 when I can, which is at least every other tankful and it gives me a warm feeling to do so, but I can't say my seat of the pants dyno can tell. The car can tolerate E25 so I doubt E10 does any real harm. There is no doubt a measurable difference but I suspect it is no more than 5-10hp and when you have 335 of the buggers does it matter?
I do understand that those with engine mods actually need 99 Ron though if they have mapped for it.