Elk aren't nearly so tough as they're made out to be. People (including me) have been killing them with 303 Britishes and 30-30's for years. Just shoot em in the heart/head/lungs/spine (and not the ass or the elbows), and they'll die from the resulting wound from just about any caliber you care to use.
That said, though -- I don't recommend you go buy a 243 or anything that small -- my personal choice if you're looking to tone down the recoil a bit from the 270WSM, would be what I currently use -- a 308 Winchester with 150 grain premium bullets (Nosler AccuBond's is what I use currently, but Barnes TSX's or Partitions or what-have you would also do fairly well). You can go to a 260 Rem, 6.5x55, or even 7-08 to reduce recoil even further, but the step down in recoil from a 270WSM to a 308 is significant -- the step down from a 308 to a 7-08 or 6.5/260 is not nearly as big a jump down.
YMMV.