I have only one word of advice, if you find the 300 WM that unpleasant and objectionable to fire, avoid at all costs, trying a 300 RUM.
The Mark Vs I have owned and fired were not unbearable to shoot due to stock design, in fact Roy designed his stocks specifically to move away from the shooter under recoil and not bite the cheek. My 378, although certainly a handful, is not in any way objectionable and does not leave me with blurred vision, neither does my 470 NE. The 470 will leave my shoulder pocket a little tender for a couple days after 20 off the bags, as I did a few weeks back when sighting it in after building a base and mounting a scope on it, but I have shot 50 rounds in an afternoon standing without any negative consequences. My Steyr 50 BMG is downright pleasant to shoot, but it has a big tank style muzzle brake and I have not had the "cojones" to unscrew it and try it without. I fear it may break something on either the rifle or me and it's just not worth it.
Recoil conditioning is something that one must work into, I have owned and shot big bore heavy recoiling rifles most of my adult life but I did start out shooting my 243 for more than 10,000 rounds prior to my first biggy. My first real BG rifle was a 7 RM so a step up from the 243 but not a leap in the recoil department, from there I branched out and had several 338s and 375 H&Hs and then on up to a 416 Rigby and 458 WM. One must also keep in mind that I was shooting CF rifle at least 4-5 times a week and going through more than 10,000 rounds a year in all calibers combined. All this shooting does tend to desensitize one to recoil. I was also going through about twice that amount of CF pistol ammo per year, and a lot of that was full max 44 RM on the silhouette range, again just more desensitization.
