Depends on what you mean by a "long poke in a hayfield". I really like my .243, and have used it successfully on about a dozen Texas whitetails. My longest shot has been about 100 yards on a whitetail. About 175 yards on a wild hog. Based on ballistics tables, I think the .243 will work well on whitetails out to about 300 yards or so. I've never shot a .243 WSSM, so I'm not sure how the recoil compares, but, if my shots are going to be 350 yards or less, I think I'd rather be spending less than half as much for ammo, and maybe invest the savings in better optics...

Edit: Just went to Winchester's website to review the ballistics charts on the two. No question about it, I'd rather have the .243 Win. Not enough difference between the two to justify the expense of the WSSM. You can get .243 Win ammo ANYWHERE for $13-15 per box...

Also, to answer a couple of your other questions, last time out, I put five shots inside a nickel at 100 yards, and I'm not even a very good rifleman... .243 definitely kicks more than my .223. I've not shot a .22-250, so can't give an opinion there. But, even so, the .243's recoil isn't bad at all. I switched from .30-06 because I'm very recoil averse with rifles and with the '06, I had to really FOCUS to keep from flinching. No problems at all with extended bench sessions with the .243.