Hi!
Britbrat...those figures are just in bench figures ...say nothing (or very little) how the engines behave in the air.
My experiences are based how engines react when flying them...in the air.
I agree that there are small differences among those .40-.46 engines mentioned ...but not anything a newcomer with a high winged trainer would notice. But for an experienced flier in a fast low winged airplane ...yes there are differences!
That's why (nearly ) all Q-500 pylonracers over here use the Webra .40 GT
Which I don't like being the Swedish MVVS importer[:@]

Best regards!
Jan K