Don't bother with the race gas. Contrasting what someone said, it WILL make you faster, but it's not a magic juice. Your car has to be tuned for it to produce horsepower and torque gains. In other words, filling your ITR up with it at the track is basically a waste of cash. As far as the cat goes, it really isn't worth the effort to strip it out. Power gains from having no catalytic converter are VERY minimal if at all. I just sold my '03 WRX (which stock come with 3 catylitic converters) that was entirely straight piped a little while ago and other than a little extra pull on the top end, it basically wasn't any faster than it was with all the cats attatched. Plus you end up with headaches like a) not being able to pass emisions and b) the exhaust with no cats will turn your bumper black in a matter of days. The only way to get that crap off is to clay bar it. My .02 for what it's worth, just get yourself a good header and cat-back and stick with good 'ole premium.

 

too high of an octane can be bad...

 

Even if you run higher octane, the stock ECU will not raise itself to run the higher octane. The ECU is designed to run 91, i.e. bad tank of gas its actually 89 instead of 91 the ECU will degrade itself to run the lower octane and never recover unless you reset your ECU. So unless you run about a tank of higher octane, racing gas, then reset your ECU, then fill up with hogh octane again then the higher octane really wont do anything.
So if you run 91 or 92 all of the time and then switch to 100 its not going to do anything but empty your mpocket faster.