Steve: have you ever had (or nearly had) any injury from shrugging? I ask because if I load up a bar with say 450lbs, I can shrug with it but my form isn't great.
No, but when I say bad form, I don't mean completely sloppy. My form is worse on shrugs than any other movement, but I'm still conscious of the muscles in my back and keeping them tight and at least trying to stay upright. I'm leaning forward by the last rep but I'm still looking straight ahead and still in control. IMO 450 is perfect for you if you can still complete the shrug but your form is bad. I'm just not a big believer in perfect form on anything. I think if your form is flawless, the weight your using is too light. Just don't get sloppy. Sloppy would be hitching...looking down..dragging the bar up your legs, bending your back to an extreme, stuff like that. Perfect form on a shrug would be keeping perfect cadence as you go up and down, holding up for a pause, having a full ROM, etc. etc.
Right now I'm using 95% of my 1 rep max on the deadlift for a 5 rep max on my shrugs. If you are actually using MORE for shrugs than your 1 rep deadlift max, then....more power to you, I've never been able to do that.
I don't understand that 'rolling the shoulders' business. I've never done that.