Kim, the dreaded Fancherized Twister ("KISS"...the blue & white job...you've seen it several times) weighs around 48 oz. now, and I fly it on 59' eye to eye lines. I have never checked the lap time, because it feels just fine. The TT Cyclone works great for me, launching at 9,700.
One thing to think about, tho. I'm running the .46LA muffler, so it's relatively quiet. If you run the stock Magnum muffler, it will be ok, but a bit louder. If you're running a tongue muffler, well, you know. The thing is, that the quieter the engine/muffler, the slower it sounds, and the slower it feels. Sound is a tricky thing. Ever timed a racer, speed plane or combat model that was really howling...but you found wasn't going very fast when you put the stopwatch on it? Stunt is the same way. I used the LA muffler to balance the plane (almost). If it didn't need that much weight, I'd use one of Randy Aero's CNC Tube mufflers with a rubber ducky on it, even if I had to add some tail weight.
Steve