Going with a big chunky muddy mary on front, what rear?

Rocket Ron?
Nobby Nic?
Rock Razor?
Hans Dampf?

I ride dark peaks.

how much grip do you want – or do you like to slide a bit on the back end?
Rock Razor or Nic out of the 4 you mention depending on the question above!
Personally rear end tyre – Maxxis DHR2 for winter and the ardent 2.4 is surprisingy good alround.

I’m edging towards nobbys, but the more I think the less I think I ride in mud in the summer. Hmmm

Definitely not the Ron- if you can get away with a Ron on the back without flatting or sliding everywhere, then you should replace the Mary. Nic is low on grip and puncturey. HD is inexplicably draggy for its uncompetitive grip and gets worse as it wears because the tread is totally dependent on its square edges, which don’t last, but at least it’s not as delicate. ROck Razor I’ve not used but by all accounts is actually good.

In conclusion, DHR2.

I’m edging towards nobbys

Surprisingly poor combo with a Magic Mary up front. Basically, the Mary highlights the shortcomings of the Nic to the extreme.

but the more I think the less I think I ride in mud in the summer.

Rock Razor on the back is genuinely the most impressive tyre I’ve ridden. You expect it to be quick, you don’t expect the tenacious grip when leant over, or the fact that it seems to grip really well when climbing on a multitude of surfaces as long as it’s not muddy. Obviously, it’s not good under braking (but then it teaches you to lay off the back brake and use the front brake more, which is good technique anyway), but otherwise it’s genuinely the best rear tyre out there for a surprising range of conditions.

Maxxis DHR2 for winter

Also a very good rear tyre, it’s quicker rolling than you might expect (though not a quick tyre compared to a semi slick), and grips just like a Minion DHF in the corners, but has better braking traction.