I believe the MK2 is gas in gun (if it was available)
MK3 will be gas in shells
Personally, from experience of using a cam870 , I’d be going for the MK3
Using standard Aps smart shells, performance will be a bit lacklustre as seen in the redwolf review.
X-power shells with their extra gas capacity would be the way forward
I would see 40+ meter range out of my Cam870 when using them, but the street sweeper has a gap between the drum and the barrel which will allow gas to escape, reducing range. So use the higher power shells