I checked in with this a little while back and meant to offer my 6.3 cents but simply forgot. I've since been sprayed with baby poo which was good enough incentive to avoid babies and get back to this for a little while.
So, heres my take -
M = rubbish
VX and VX3 = over-hyped. rubbish (though not horrible for turbo applications).
K = good
H = better than K. Loves to rev. Rubbish in an auto car.
What you gain up the top of the rev range (with the H), you'll lose down the bottom.
From a practical point of view. Your days of being able to dawdle at walking pace around a supermarket carpark in 2nd gear are just about over if you pop the H in. (unless you have a 3.91 maybe or shorter diff ratio)
So, here you are driving around the supermarket carpark in 1st gear now, with your loud exhaust and the thing is popping and banging with the slightest lifts off the throttle. You'll Iook like an idiot. (I've been that idiot).
If you can get over that or take another car to Coles or Woolies, then you're good.
Here's some useful data though -
K Grind camshaft -
Used in high compression B23E engines in Europe, Australia and Canada.
Easily available in Australia, found in most B23E engined (except 242GT) cars up until 1985. Peak torque at 4500rpm. Better suited to a naturally aspirated engine.
H Grind camshaft -
The most aggressive factory Volvo cam. Found in early B23E engines (242GT) in European and Australian markets. Not available in US market.
Much more powerful than the ‘K’ grind cam near the red line, with trade-offs of lower low rpm torque and higher fuel consumption.
This is the only homologated cam in Volvo Genuine Cup racing.
Probably not really suited to a turbo application.
I put together a factory camshaft article for the VCOV magazine a few years ago, covering all the factory camshafts known at the time with as much data (and actual experience, rather than internet-wisdom) as I could collect.
Let me know if you want a copy of the full article.