This has been a very interesting discussion and in many ways far more insightful than the usual "what calibre". Fundamentally most calibres in the 243 through 270 to 30-06 with a muzzle velocity of 2450 fps plus, is perfectly good for any deer out to reasonable ranges.
But the sighting equipment is what really makes the difference and has a very real effect on how well you can put that bullet in the right place.
Joking aside, Red-Dots Iron-Bru can once properly cable tied and zeroed is probably good for about ten yards, although a bare barrel or open sights would extend this distance.
Once we get into scopes the choice is usually dictated by what the rifle is going to be used for. I think the best route is to have:
one rifle set up for hill work - flat shooting calibre, good from prone, mounted with a bipod with a 4-12x42 or 50 scope
one rifle for woodland / farmland - easy to shoot off sticks, quick handling - 6x42 is a good starting point but a zoom in the 1.5 - 6 or 8 x42 sort of size might be better.
one heavy barrelled varmint rifle - small flat shooting calibre with a high powered - x56 large objective, or even night vision - for shooting foxes at longer range at night
But for most of us three or four rifles is not an option - budgets don't stretch to that.
I don't think there is a true allrounder, but feel that quite a few of the latest generation scopes that have a 5 or 6 times zoom are worth a look - the z6 1.7-10 x 42 can be mounted nice and low, can be wound right back for close range running game, but then zoomed for a longer shot. But cost is high. If I was buying a new scope today I would probably go for Z3 3-10x42 - as its nice and compact, but will still have enough reach, and yet good enough light transmission for last light.
But I am blessed with good eyes and don't feel disadvantaged with a 6x42.