ORIGINAL: UNBALLANCED
I've got an OS 25 FSR in mine - balanced without any additional weight. Goes vertical (slowly) with a 9/4 prop. The plane is very very fast. I cannot imagine this plane with extra weight and more power. You're more of a man than I am if you try this combo. One word of advice. Re-glue the firewall. Mine came loose after 3 flights. Good thing it's dovetailed.
I started with an OS 25F ABC, a slightly more powerful version of your 25 FSR. It did pretty well, but I wanted more. Balance with the .32 Webra that's in it now was basically the same, but the overall speed is even faster. I've got a 10x5 on it to try to keep it slower. I was playing with the climbs today and found that vertical is essentially unlimited.