Octane is little more than "unburnable" stuff which allows you to run more timing and/or compression without getting into preignition/detonation. For real comparisons, you need to look at burn rates, density of the fuel, etc.
Here's a good resource for additional info on fuels. (I became aware of this page more than a decade ago, and I doubt it's been updated. It's possible that some formulations have changed, so check with the manufacturers):
http://www.smithtex.com/racing/fuelcomp.html