aviation gas

[2T Institute]

Be aware though that avgas is exactly that, formulated for use at altitude.
The high octane rating is all good but apparently it falls short in a few other areas.

Exactly.Avgas is made to stop planes falling out of the sky, not to make HP. You make more HP with unleaded fuels when you set up for them. avgas and ULP require different set ups which is why I can never understand the 'half pregnant' 50/50 mixes.

From my understanding people run the 50/50 mixes to get the higher volatility of pulp and the higher octane of av.
What do you think of BP's 98unleaded? seems to work pretty well for me, just ran a tank through with my reset squish and all the readings are good.

Some quick maths 98+100/2=99 so no net gain there. The fuels require different set ups and with a 50/50 mix you can run either ideal set up for avgas or unleaded.
Tuning for the fuel is the trick.  BP is pretty good used it for many years, though we have a better ULP now.

[HCE]

I have tried different pipes, needles, main jets, pilot and jd jet kit in my yz250.  None of them compares to the difference 50% av gas makes.  Race gas may be better, but avgas works, easy to get and relatively inexpensive. 
Best thing to do is try it and see.