I think the recoil of the WSM is a little bit less. The of course, depends a lot on the individual gun, cut of the stock, type of recoil pad etc etc. I have shot Browning A-Bolts in both, and thought the WSM was a quicker sharp kick, while the WindBag was a longer whallop.

Performence wise, the WSM wins on paper. Buton target and on game, I don't think it makes much of a difference. If the WSM fits him better, then thats the way I would go. He will be much happier with a rifle that fits him well.