Adam,
I have a Saito 80 and an OS 70 surpass II. Both are excellent engines. Since you have had good success with the OS line, I would stick with the OS. Both engines were flown in my Twist. The Saito seemed to be overpowered, and the OS has more than enough power. The OS 70 is in there now and will stay there as I think it is a good combination.

Waldo has the OS 70 in his as well and can give you more of a report on it than I as he has had more flying time on his. I have the same weather pattern as Waldo and it has been absolutely terrible around here for flying. At least he has gotten out in the yard or at night to fly something. I on the other hand have not due to workiong long hours at my job and this wonderful weather. The only stick time I have gotten lately is on G3 and that is starting to get old. G3 is good to keep the thumbs and reflexes in shape but it is not the same as the real thing. Have to see if I can get a nitro smelling candle to burn while on G3 or maybe go run some engines on the test stand just to get that nitro smell fix.