heres a comparison of 3 calibers , .243-7-08 and 280. The .243 has about the same or better coeficciency, has more speed even out at 3-400 yds, and is flatter shooting, the only thing the larger caliber has on it is more energy which would only help if you were to hit the shoulder bone on a deer. I use a .243 Win and use Hornady bullets in 100 gr. I have dropped big hogs with complete pass throughs at 200+ yds. I'll take it over almost any caliber.
Your friend is gonna love his WSSM. You have to understand the .243 was a wild cat, it's just a .308 with a 24 cal. bullet on the end, makes for an awsome round.
link to caliber comparison