I have modded my MK2 - internally and externally - to a level that buying a new bench rest performer cannot justify.
but I like the M4 improvements...
Welcoming the best the upper back plate dovetail feature that can slide the pic rail forward-backward.
Bench rest shooters prefers to sit more "behind the gun", for a decent eye box always better to slide the scope closer to eyes.
The angled grip not so much, me a vertical grip guy.
The trigger was working for me well with a vertical grip, I like the new adjustable LOP.