Hey bud, I have a twist and it had a OS.50sx. I flew it with a 12.25x3.75 and 12x4 APC props. It was flown with 10% fuel and would pull out of a hover, but not very well. If/when I screwed up my hover I always would roll it into an upright position and fly away. I wasn't able to really muscle it out of a problem. Even with that said, the 50sx is a great engine for fun-fly stuff. It is in fact the combo I used to do real well in my first fun-fly. I have since gone on to a paul swany "MOJO" and I am using all the gear from my twist for it. Another engine you might want to look at is the Mangum .52xls 2-stroke. I ran my .50sx a little lean too many times and it has very little compession now. I bought the .52xls to replace it and I couldn't be happier. It runs exactly like my 50sx did when it was healthy and actually pulls harder. I paid 79.99 thru tower for it a little while back and about 150.00 or so for the OS. I'm not sure where you live but if your close I do have parts for a twist if your interested (Wing, fuse, etc) I will pretty much give it away.
Your going to love that twist you got, it has been my favorite plane so far and I really hope I have as much fun with my new one as I did with it. Feel free it PM me if you have any questions.

Dave