RE: recoil on single shot 20 ga. vs .......
The .243 is very popular with youth and women hunters for deer sized game. The other chioces are good as well. It is also excellent on smaller game because it shoots pretty flat.
Sometimes it really depends on the weight and design of the rilfe. I had a savage 110E in 30-06 when I was a teenager and weighed like 90 pounds. It spun me around a little when I shot it, but nothing I couldn't live with. I would say slightly worse than my H&R 20 gauge with 3 inch magnum field loads (those shotguns are pretty light).
Now I bought a remington carbine pump for my step father (7400?). I think it was the one they discontinued and then brought back. This was also a 30-06 but a shorter prettier gun than my savage. Totallly different animal! I hated shooting it pure and simple. It kicked so hard it made my teeth hurt and I would rack another shell from the recoil. The only thing I have shot that is comparable would a be a 3 1/2 magnum turkey load out of an 870.
I also had a 8 mm mauser (military) that was very easy to shoot, and that is simular to a -06 as well from what I understand. I think it really depends on the weight and design of the rifle.
Paul