RE: is it possible?
Best combo so far for the OS55 has been with the 11x6 APC and jett-stream muffler. Turns around 14,500-15,000 rpm.
A 12x7 is WAY too big, even for decent aerobatics use. Regardless of the muffler, you want that engine to turn up around 13,500 to 14,000 rpm ground peak to develop real good power. So far, 11x5, 11x6, 12x4, 12x5 seems to work well. The 11x7 is not bad, but definately does not work well with the Jett-Stream installed (pulled rpm down too far).
And if you are looking for just all-out speed on the revolver.... try a 10x7 or 10x8 .... just be patient while it gets up to speed on take-off.