RE: What do you think of FORMOST 150 ?
Flying a P-80 in mine as well. There's enough residual thrust from the engine to make the airplane a real floater. The flaps will help some, but you will need a lot of throw to get enough drag to make a real difference. I used full span flaperons for awhile which helped, but still could have used more drag. Right now I've scabbed on split flaps under the wing stubs and they provide more drag but still not enough for my taste. They also cause a lot of ballooning which needs a chunk of elevator offset. The flaperons caused a pitch down effect. Really, it needs a speed brake with this engine.
If you haven't done it yet, it would be worth your time to put an incidence meter on the wing and stab. I had nearly 2 degrees of right wing LE up incidence which has caused no end of roll problems. I've gotten a lot of it out, and it's better, but it's still not right. I ended up shimming the stab up with a couple washers under the aft hold down bolts. I think the booms are also cocked a little sideways.
I did not shim my P-80 for up or down thrust. The accel/decel checks I've done seem to show no need for thrust adjustments. Of couse, all the other stuff not being straight could be masking anything. 167 flights so far.
BTW, Nitro has them back in stock along with a smaller one.