I didn't have time yesterday to add details, but here's my thoughts on the two covering the areas that are important to me:
Accuracy - tie.
Harmonics - Crown has a slight edge over the MKII.
Weight - synthetic Crown all day long.
Power - this is where is gets complicated:
- Out of the box, the MKII has the edge over the Crown
- Modifying TP & Probe and adding hammer weight - my Crown has shot as high as 74FPE, and I've only been able to get my MKII up to 68FPE
- MKII will accept a larger plenum easier and more ergonomically than the Crown, with this - MKII by a mile
- The Crown's reg has to be cranked up high to shoot medium weight lead (27-33gr); the MKII can do it with less reg pressure, but again - I hit some upper limit already with max velocity
Length - MKII

. The shroud will be in the scope view at lower magnifications on the Crown, not a big deal unless you're really needing <=6x magnification. With the 700mm MKII, using a low NF unimount with my 4-32 scope - the big fat STO Mus moderator isn't visible at all at 4x.
Maintenance - Crown

. Less areas for leaks, less parts / o-rings.
Ergonomics - I prefer the Crown for both hunting and BR, I have also always felt the Impacts were built for BR - but this is all very subjective and everyone will have their own opinions.
Shot count - MKII. I get substantially more shots with the MKII than I do with the Crown, regardless of what I shoot.
Tunability - MKII. You get the extra valve stop feature and it's less work to mod the screw in the hammer spring tensioner.
So why did I get an MKII? Simple - I'm planning to use it with (22 cal and .257) ammo far heavier than the Crown can handle. The Crown can handle 36gr (.22) without additional plenum volume, but that's really pushing its limits.
The 700mm Crown is perfect for 24-30gr, it's just a shame that the factory 380mm barrel doesn't spin heavier ammo right, the power IS there, but it doesn't appear to be compatible for anything above 18gr pellets.