RE: P-51 Mustag
The P-51 sound cool, but if you want to go faster than the P-51 and still be able to land at a slow speed just mount that .21 on the back of a Kavan Projeti. I've got one with a .25 norvel on the back that will take an equivalently powered shrike's lunch money! If you get my drift. Who sells that .21 I may want one for myself. If your P-51 is the Herr kit than you've got a good plane, but its not quite built for the kind of speed you may have in mind. Pica makes some nice 1/12 scale war birds that would be a great match for a hot .21 or .25 engine.