Dave,
Have built and flown the Mid-Star 40. Powered it with an OS .46. It flew GREAT and damn fast. I loved it. It had an untimely demise when I made a mistake and lost sight of her in the Sun all at the same time. I then built a 4 Star 40 and powered it with an OS .46 also. The 4-Star is a good airplane but it isn't as fast and doesn't seem to respond as well as the Mid-Star. It's a SIG, you can't go wrong