RE: correct prop - os.91 fx ringed
Vivek, based on my experience with about half a dozen Fx .91s, they are pretty tolerant of a range of operating rpm - the ones I have worked with have been happy between about 9500 and 12K. Try out a few of those props and report back which one flies the model best. Sometimes just trying stuff out is better than seeking internet advice - propping a plane is a good example.