The problem isn't so much the actual octane rating, but the consistency of the fuel.
Once you start mixing with pump gas, you're not going to know how much ethanol is in the gas and your jetting will vary from tank to tank, regardless of how precise you mix the pump gas and race fuel.
It's NOT recommended unless you get a large quantity and jet for that load of fuel only.
Once you run out, buy another large quantity and check your jetting or re-jet accordingly.
Only buying 5gal of pump gas at a time is a great way to inadvertently get too much ethanol in the mix and melt a piston.
Most of the time there's no way to talk a guy out of going down this road until something breaks, so all I'm going to say is KEEP AN EYE ON YOUR JETTING!

Generally you can run race fuel a tad leaner than pump gas, because the ethanol in pump gas requires more air to burn (making the engine run lean).
Another point to make is that you can get closer to stoichiometric ratio with race fuel because it has less tendency to detonate.
With pump gas you need to jet fat to reduce detonation problems.
Just give her a run with straight race fuel and see what the plug looks like, if it looks good then keep it there.
If you want to tune it to the T, you have the option to, but for overall performance and longevity, jetting is best left on the safe side.

Generally you can run race fuel a tad leaner than pump gas, because the ethanol in pump gas requires more air to burn (making the engine run lean).
Another point to make is that you can get closer to stoichiometric ratio with race fuel because it has less tendency to detonate.
With pump gas you need to jet fat to reduce detonation problems.
Just give her a run with straight race fuel and see what the plug looks like, if it looks good then keep it there.
If you want to tune it to the T, you have the option to, but for overall performance and longevity, jetting is best left on the safe side.

Best powers DOES NOT occur with a stoichiometric ratio.  In a four-stroke best power usually occurs some where in the 12.5 to 13.5 A/F ratio for naturally aspirated and 11 to 12.5 in forced induction four-strokes engines.  Stoichiometric mixtures pairs up all of the oxygen atoms with all of the fuel molecules in the correct proportions so that there are not any fuel molecules without a dance partner.  Increasing the amount of oxygen that is trapped in a given power stroke is what high engine designers are constantly striving to do in their quest to increasing the power output.  Oxygen is the scarce commodity that we want to find a dance partner for…..  We have to slightly over fuel the mixture so that ALL of the oxygen atoms find dance partners.

In a two-stroke best power will fall somewhere in the 11.5 to 13 A/F ratio.  It depends upon the trapping efficiency of the engine.  The trapping efficiency depends upon the port and pipe design and how well the ports and pipe are working together. 

Two-stoke A/F curves are not flat like a four-stroke curves and do not run the same A/F ratios as four strokes.  Unfortunately, this is what is being taught at the tuning classes offered by one of the dyno manufactures for their new dyno owners.  Do not let anyone put an O2 snifter tube in the stinger or silencer while jetting your two-stoke engine.  We have to replace many pistons and re-tune a lot of two strokes that have been tuned by their graduates and the shops are that are certified tuning centers from this school.

Stoichiometric ratios are more theoretical in nature and will produce the least amount of emissions.  Our cars and trucks will run close to stoichiometric when cruising and idling.  Most of the high performance four-strokes I work on, will start to show a power loss or go into a lean miss-fire at around 13.5 to 14.5 to 1 A/F ratio at 1/2 to full throttle.