I guess I never mentioned it, but I use Fed 210's, but I never plan on shooting it at temps below freezing.
As far as starting over.....just get 1 lb of H4350. Start at 58 or 59 gr, load em 1 grain apart (59, 60, 61, ect) to 64g. Just three shot groups...nothing more. If you don't see any PSI signs, kick it up another gr., ect, till you hit the end. I like to KNOW where max is on all of my guns. You are bound to see at least one good group on your way up. When you do, load up three or six more of that load, along with three up a 1/2gr and down 1/2 gr. Load em out as far as you can and still fit in the mag.
Now, as far as your bench setup.... Beg, borrow or steal a front rest and rear bag from someone for testing. Be sure to remove your swivel studs .....they get in the way and tear up bags. If your forend is way narrow, try setting a leather glove on the bag to help snug the stock in the bag and keep the front of your gun stable. Or buy an "accuracy asset" for your stock....look it up.
The next paragraph is only my opinion...learned from thousands of rounds off of the bench with both hard kicking hunting cannons and benchrest guns.....the guys can flame me if they want about it....I have enough tropies on the wall (both the fake wood kind and the furry kind) to prove that it works for me. I have shot more bugholes with "poor shooting ***'s" that my friends give me to "work on" because thay can't get them to shoot. The answer....Poor bench manners on their part....death grips....flinching...no idea about paralex,....ect.... Skip over it if you would like.
I am not sure how tolerent you are as far as recoil, but try not to hold the gun in a "death grip". When I am bench testing my hard kickers, I give myself a little room as far as the scope goes. I only have the trigger hand on the gun...the "free" hand is the bag squeezer, not the gun holder. I slide my face back away from the scope....way back. The further back you go, ths smaller the field of view is in the scope. I am usually back far enough so that only the bull is showing in the center of the scope.....maybe 1/2 the field of view. This gives me some assurance that I won't be a bloody mess for the ride home. I am not talking about free recoil, just NOT a death grip. And if I lose the ever so important "cheek weld"...so what, we are on the bench...cheek weld just messes up accuracy when shooting from the bench. Also, make sure that you hold the gun the same for all the shots....just because the cross hair is on the mothball doen't mean that the gun is in the same position on the bags. Try to wiggle and jiggle and slide the gun into position the same for each shot....this is HUGELY important with a hard kicking hunting gun....because the gun will be actually moving a fraction before the bullet leaves the bbl...you want it to move the same each time.
I am sure your WSM will give you several thousand rounds of accuracy. If it takes several hundred rounds to find the "special" load, so what. If anything, it will make you a better shooter, and give you LOADS of first hand knowlege about handloading...not to mention that it is BIG FUN!!!
Keep us posted.... All good stuff.