Didn't vote. Thought I'd offer some thoughts, though.
The only reason I even bought a G27 was that I unexpectedly came across a deal on a barely used one w/night sights that was simply too good to pass up, and I thought I'd probably adapt to it since I already had a G26. I simply like the G26 better, all things considered. It was my first choice in buying a subcompact Glock, and after having owned both I'd again choose the G26 if faced with the same choice.
Anyhow ...
I've handled and fired a MK40 a bit. It was owned by a cop from another agency whom I qualified a couple of times.
He'd initially brought it to the range NIB to qualify with it without having even fired a single round through it, so I suggested we shoot it a while before he qualified with it. After shooting it himself he seemed to really welcome the idea of me doing a lot of shooting while 'breaking it it' ...
... and I didn't mind, so we spent some time shooting a bit over 3 boxes of standard 180gr JHP's through it before I ran him through the standard course-of-fire.
Having handled and fired a K40 off & on, I can offer that the MK40 doesn't 'feel' all that much lighter in the hand, but it seems to have a noticeable amount more snap & muzzle whip than the larger K40.
It seems to have more snap & whip than my G27, too. I'd expected the all-steel MK40 to have less felt recoil than the polymer G27 subcompact ... but there you go. Subjective perception at work.
The next time I ran into the cop who owned the MK40 I asked him how he'd been adapting to his little steel gun. He didn't seem much more enthused about it than the last time. Apparently, both the felt recoil and the heaviness of the little gun hadn't turned out to match his expectations.
Each potential owner might benefit from trying examples of both for themselves before making up their minds.
Oddly enough, while I chose to order a SW99 Compact chambered in 9mm, after having handled and fired a couple of them chambered in .40 S&W, I plan to order a M&P 40 Compact, instead of a 9mm model.
Never said I was consistent.
I own 4 pistols chambered in 9mm and 4 chambered in .40 S&W, and I've carried issued pistols chambered in both calibers, as well. I have various preferences which are satisfied by different makes/models/calibers, depending on the time & circumstances.