K3 for me. Depends if u need the higher resolution. Also the K5 has its memory card next to the front camera. I preferred everything routed to the drive under the seat
1080p or 4k is fairly irrelevant as innov use high compression making the 1080p closer to 720 in quality.
Ultimately as long as if is good enough to read a number plate which the K3 is.
I have the older K2 and prefer the mem card under the seat.