No offense taken and I'm going to disagree with you here for the sake of learning something...if I end up being wrong at least I'm walking away with a better understanding of this.
First off I have limited clearance between L4 and L5...I piss them off and vertabrae is sitting on nerve and life becomes very unpleasant.
In lieu of GM's, I do alot of SLDL's off of boxes using various rep schemes, sometimes light sometimes for 3-5 reps. I think my best is somewhere around 500+ for a triple.
When I do GM's, I end up having to use excessively light weight in order to actually feel like it's hitting things right. I'd be lucky to triple 315 from the seated position.
I know one roadblock for me is the awkwardness of using a regular barbell. Westside uses the SSB quite a bit. I've experimented with the manta ray and it makes it a little easier but not by much.
I feel like the GM puts way too much stress on the lower back because of the bar placement...I'd say "law of torque" but I'm not referring to twisting forces. It's the difference between holding a 10 lbs. plate in your hand and putting a 10 lbs. plate on the end of a broomstick and holding the opposite end (sledgehammer trick). That's what I feel like is happening with the GM. With the weight high on my back and the bend at the waist, all of that stress is multiplied and placed on my lower back, versus a SLDL where the broomstick isn't quite as long, resulting in less stress.
The logical answer would be to reduce the weight, just as you said, but I'd expect there to be some correlation between SLDL and GM if you know what I mean. And if I'm only able to handle less than half of what I can using an SLDL, do you think the GM is really that beneficial in this case?
I heard alot of people screw up the JM press and they don't feel it in their triceps, and the answer provided for that was "if you don't feel them, don't do them." that's where I am with the GM.