Hi Mark.....
The W-50 is a heck of an engine. Runs pretty darn well. Considering the availability in the UK, and Alan's support of the product, its a hard package to beat. No doubt lots of folks have had sucess with the magnum/W50 package.
The top end Jett product in that size class is the SJ-60LX (or BSE-60LX if you prefer). It is set up for serious top end performance, and includes the SS type muffler. Usually a 9x9 or one of the 8.8x9.25 props works very well (clipped a bit if needed). Sometimes a clipped 10x10 can do some wonders too
It can squeeze out a little more if you go with a full size nitro pipe. But with the peformance it has with the standard setup, most folks stick with the less complex arrangement and use the standard SS muffler.
Bob