First, Let me thank veryone for speaking up. Next,let me let you in on my flying style. All I can say,is that it is a pretty agressive sport aerobatic, folllowed by a bit of 3D. I don't hover for 4 minutes at a time, nor do I beat the crap out of a plane all day. Even on the ground I recognize the linear performance of the 4 stroke, but remenber 2 strokes are what I'm familiar with. I have no problem with givng 2/3 open barrel to get 1/2 of available power. NOT THAT I THINK THAT'S BEST! I fly whatever the plane needs.

Fuel wise (locally) my choices are Cool Power, Omega, and Wildcat.

YS engines are easily the best, but not an option. $$$

tnewman-I'm not picking, I really liked what you said, just please elaborate.

basmntdweller- you may have hit my problem too.
My biggest headache with a 4 stroker is I can't hear it running. I want to hear my engine all the time I'm flying. I have a Saito 91 in a GP Super Sportster and it's the sweetest flying plane but I can never hear the thing. I grew up hearing these things scream and it just doesn't seem right being so quiet.
Any body got a comment.. Other than "Get over it!".

weatherly-In mine i had a 75 supertiger w/ a slime line pits muff.
I could do vertical snaps as high as i wanted, flat spin, invert flat spins just what ever you wanted. If i had my choice i'd damn sure go w/ the 91 FX..... In my opinion i think you hate life if you go with the 4 stroke....

CRAP! Did I mention I had a ST 75 (with a slimline) in the basement? Now the 91 is still winning based on familiarity.

tnewman-That's not the issue you wanted to see the motor really shine......then stick some nitro in it.

I like that comment alot. Saitos do well with 30%

I appreciate this comment the most so far.

I need explanation:
tnewmwn-Also you don't want the 4 strokes turning those high RPMS above 10K they work harder and get better when running down in the 8800-9500 rpm range
??? A 15x6 at a certain rpm equals a 15x6 at a certain rpm, right? Please see what I said about barrel opening vs RPM.

Another thing you can't look at a specific prop and rpms to determine power. Props are different and the 4 strokes like bigger props because of the power and grunt in the middle of the throttle.
15x6 is all I intend to do.

Not to pick, just I'm looking for the best 19 to 24 ounce power package. That's it! As of today, I do not have access to a cold fusion electric motor, so I've got to look elsewhere. At 10% to 20% nitro what can be done? Remember, I want an aerobatic plane (6.5 pounds), with a 14 to 15 inch prop, and reliable ( and quick) throllte response. I'd like the most static thrust I can get, with the two prior priorities addressed.

So,
14(or 15)x6 APC on a Saito 100?
14(or 15)x6 APC on an O.S. 91 FX?
Any other input?