The major difference is the 109 is not like your 110. The 109 is oxygenated. This makes more power and does burn faster than the 110.
This struck me as odd because my understanding of octane made me question why there would be such different burn rates for similarly rated fuels. After a little research, as it turns out, Sunoco 110 has an AKI of 110 (115 RON, 105 MON), where as, MS109 has an AKI of 105 (109 RON, 101 MON). So yes, I see why there is a different burn rate now.
Comparing MS109 (105 octane) vs 100LL (from what I can find 103.2 RON, 100.5 MON, basically 102 AKI), you'd get an increase in AKI with MS109 and the benefits of oxygenation. So you might be able to squeeze out a little more compression and/or timing with it.
I have access to 99.99% pure methanol. It contains about 50% oxygen and an AKI of 119 (133 RON, 105 MON). I've been very tempted to add it to my fuel, but the loss of BTU's is what has held me back (plus concern with oil mix compatibility). Basically, methanol is half the BTU rating than pure gasoline (125,000/gal for gas, 64,600/gal for methanol). Maybe I'll mix up a gallon of 89 with 10% methanol and see how it performs (I just switched over to Amsoil Interceptor at 50:1, should be fine). That will give me just a bit over 92 AKI and about 118,393 btus/gal.
Does anyone else really think about this stuff? A lot of times I get bored at work and sit down with a pen and calculator and figure up mix ratios and levels of BTU and octane. Guess I'm just a nerd at heart.
*EDIT* And for anyone who wonders what methanol and MTBE have to do with each other, MTBE is processed using methanol and isobutylene.