A stationary prop creates less drag than a windmilling prop - any qualified Pilot who thinks otherwise needs to revise his forced landing procedures before he/she flies again IMHO
A tale I've related on here before:
I spent ages agonising whether I should try stopping the engine aloft to properly simulate the glide. Eventually I decided I was going to do it, so climbed to 8000' over a local farm strip (where I often do PFL's right down to landing), then idled back down to 7000' to cool the engine a little (Rotax so water cooled but I decided to be gentle as possible) before switching off.
First thing to report was that I had to fly really slowly (almost to the stall) to stop the prop windmilling. Once the prop had stopped however, the decent rate at best glide speed improved (ie decreased) significantly, but was still greater than a normal idle glide. Had great fun gliding around for ~ 5 minutes, experimenting with different speeds to find the optimum glide speed, found it to be more or less what the POH said it should be. Also cycled the wobbly prop, was great for adjusting decent rate without retrimming, could be very useful in a real forced landing.
Finally decided to restart by windmilling - had to dive to 120kts before prop started to turn again, but the engine fired instantly.
Very useful experience IMHO, I now know the true glide characteristics of my aircraft should I ever face an engine failure. No doubt a controversial action though, cue loads of posts.....