5S-FE fuel?, What fuel to use? Options

[UVZ164]

Hey guys, I'm kinda new here and not sure if this is the right place to post this.

I did a search but couldn't find the specific answers I wanted so I thought i'd ask.
I live in Sydney Aust and the fuels available to us are: E10(10% ethanol) 91 octane, and regular 95 and 98 unleaded.
I recently bought a ST204 ZR which is the equivalent to the American GT. It runs the 5S-FE.
The guy I bought it from told me to steer clear of the E10 as it will ruin the engine. As my wallet isn't that deep I decided to give the cheaper E10 a go.
After about a month and a half of running the E10(i'm assuming the previous owner used 95) i'm beginning to hear a noise almost like tapping when I rev the engine above 3k rpm and just let it decrease naturally. As it never made this noise before, could I be right in assuming that the E10 is doing something and possibly ruining the engine? The owners manual states that 91 octane is as low as you can go but it doesn't say anything about Ethanol.

Thanks in advance,

Reece

[k-weaver]

There is a lot of good information in this post in regards to fuel. I'll be the first to say I pump 91 into my tank. A while back ago I tried 87, 89, and 91. I noticed no power difference whatsoever between the three. What I did notice however is that on lower octane fuel my exhaust would pop on decel. Once I started running 91 my popping decreased. I still get the occasional pop in the high RPM but its not as much or as loud as it was when I ran 87.