Premium, Super, High Test, etc. is usually referring to the highest octane fuel sold at your local gas station (91 to 94/95 US octane). Some stations have a middle octane fuel somewhere in the 88 to 90/91 range. Regular is usually 86/87 octane.

The ideal octane is the lowest octane without producing engine knock. The manufacture should know what's the best octane for their engines. The owner's manual should have the recommended octane. If I had to guess (which I would not), from the information I've read about the Toyota engines (9.something : 1 compression) I would think that to play it safe I would use at least the middle octane gas and keep an ear out for any knocking. Best and safest bet is to follow the manufactures recommendation. There is definitely no need for 100 octane fuel!

I have a motorcycle with 12.5 :1 compression and it runs best with 89/90 octane. The manufacture recommends 92 octane so I use that most of the time, but when I 'm going out to play I use the middle grade fuel. I must tell you that I do not guess at what is best. I have a power commander, a device that is integrated into the engine's fuel management system so I can reprogram the timing and fuel mix. I can manually adjust the air/fuel mix and timing for the engine at 500 rpm intervals and at different throttle positions, from idle to the rev limiter (12,800 rpm). To take the human factor out of the equation, You can link this system to an automated computerized dyno, using an O2 sensor in the exhaust. It runs the motorcycle through a 2 hour program to determine the exact settings for air/fuel/timing at every rpm and throttle position (for about $300). It even simulates a load on the engine like you actually driving. After this is done the settings are downloaded to the power commander and you end up with the exact fuel/timing map for your engine. The trick is to do all your modifications (cams degreed, head work, boring, stroking, turbo, changing to less restrictive air filter and exhaust, etc.) before you have this done. This takes the time consumption and guess work out of the achieving accurate settings.

Koz