I've used the Lead Sled as well. It works well to take the sting out of recoil, but can beat up the recoil pad on the rifle. My friend's Savage .375 H&H suffered some recoil pad damage, but it's a pretty cheap pad to start with.

I have shot my friend's .338 RUM, with the R3 recoil pad (same as the Limbsaver, I think). It is a nice pad. The Decelerator is an old standyby, and they still work well too. I've shot a 12ga trap gun with a Kick-Eez pad. It's a nice pad, but it's so soft I am afraid it won't hold up well in the long run on a hunting rifle.

Another friend has a Pre '64 Model 70 in .458 WM. He uses a 25# bag of shot between the gun and his shoulder. Personally, I've never tried it, but he swears by it. Sounds like a pretty inexpensive fix, if it works.

I don't envy you shooting that .378 Wby. A friend of mine has one, and it wasn't pleasant. I recommend shooting it in the off-hand position first, at least until you know what to expect.

Good Luck!