I have used all sorts over the years, from 22 to 2 bore, when I was clearing deer for a living it was the .243 I used and at the time I had, 243, 270, 7X57, 300wm and bigger.
I have said it before and Ill say it again, using the 243 and GKs shooting roe and reds I have not had a single deer run out of hundreds shot, the only deer I hit with the combo that ran was a Sika stag shot at very long range because it was already injured and hit in the boiler room it ran 50 yards.
Strangely all the deer Ive had run on, have been right through shots in the H/L area, yes there was a blood trail to follow, but I would far sooner get drop to shot. And before anyone says " yes but your shooting smaller animals, well I shot Red/Roe in newly planted forestry in the north Highlands[most on the lamp] Muntjac, Roe, Fallow, Reds in Suffolk, Same in Hampshire with the addition of Sika. The only animal I would NOT shoot with the 243 in the UK is Boar.