What is lap time? I have a Sakitumi that is a similar weight, LA.46 and flew it a lot with the APC 11.5-4, 11-4, and 12.25-3.75. It seemed to want to wind up with all of these, and up top tension wasn't the best. I tried the TT-11-4.5 and have been happy since. I think I have it turning a few more RPM but still in the 5.5 second range and tension is much improved, speed more consistent. I like that plane a lot now. Try the flatter pitched props again with more RPM. If tension is better but lap time too fast, go to two foot longer lines. Search on here or on line for the Paul Walker trimming flow chart that was in Flying Models with the Impact article. Must reading for everyone, even those that only occasionally do a loop or two.
Type at you later,
Dan McEntee