RE: O.S. 91 VR-DF
My general suggestion to folks looking for a high powered plane that can exceed 150 mph --- is to build it yourself from scratch/kits/plans. Modifying an ARF is usually not a good option.
With an ARF there are too many variables - by the time you get done stripping the covering off, beefing up the firewall, ensuring the wing structure is suitable or is beefed up, making sure the tail (usually the first thing to fail) is up to the flight loads ----- you might have just as well built the plane in the first place.