Not knowing much about the mechanics of sailing yet I can only go on my observations but in light winds our M certainly is faster on the GPS at or less than 10 deg but at 15 knot winds it seems better with fractionally more.
I tried to screw it up by tightening up but the GPS said it was actually slower or of little benefit, maybe just my inexperience.
After sailing for several weeks with other M's (both models) and X's with a Mack 28 as well I would be hard pressed to say that any were better than another, it just depends on what you want to achieve.
On several occasions I did note that even though I was the most inexperienced sailor and was pulling a very heavy aluminium dinghy I could pace the X's but two M's left me well behind and the Mack 28 went by in a blur (well not really a blur but)
As for powering, load and the correct prop seems to make a hull of a lot of difference, when loaded up I change to the Hydrus prop but as recently we did a trip power only, we changed to the high speed prop for more speed and economy whereas under load the reverse would be true using the same prop.
You have to compare apples to apples and unless all the parameters including aims are the same the results will be different.
I always liked the idea of the swing keel but after having a couple of senior moments and forgetting to lift all boards, I think the stiff DB may have saved the flimsy rudders. Even with me telling the wife to gun the motor

we just sat there and spun until I decided something was not quite right, really must learn to wait until beaching before breaking out the Queensland diesel (bundy rum).
Really like the easy access and open cockpit but also like the easy access to the large aft berth too.
Really liked the idea of the shower in the X but extra moisture in the boat in 98% humidity is not good either.