I think 8*40 are pretty much optimum for full sized 'nocs. Mine are Leica ones and pretty expensive even secondhand but they are, as you'd expect, excellent. Now whether they are genuinely that much better than other pukka optical brands like Nikon or Olympus at half the price etc is perhaps debatable. 10x are quite a bit harder to hold steady, even whilst bracing your arms, and, other things being equal, you'll usefully get a wider field of view with the 8x. For the "mature" chap, there's little point in 7x50 even at night as, for technical reasons (exit pupil) only young eyes can benefit from the extra light gathering.
I also have a pair of minature 10x25 (also Leica) but 8x20 would have been better. I went for the 10x25 for the better light gathering rather than the magnification but slightly regret it. There's a lot to be said for the minature ones, particualrly top quality ones like Leica or Zeiss, which aren't quite as brutally priced as full size ones, in that you can stick 'em in your anorak pocket without them being a burden. You only want the 8x42 if you are specifically going to look at stars or birds or whatever
For full sized 'nocs, strongly recommend 8x40 or thereabouts, as good a make as you can afford /justify.
For even more pocketability I have a Zeiss 6x18 monocular which is pretty handy too. Secondhand it wasn't too expensive but are pretty dear new
