Lamb Grain vs Grass

Ive been reading and researching about the differences in Grain vs Grass fed ruminents. today I and my brother Scott would put this to a taste test myself. Both were vacuum packed loin chops. Upon opening both packs, the grain feed lamb exhibited a strong sour smell where as the grass fed lamb was somewhat neutral. Both the grass and the grain meat showed equal levels of good marbling and fat covering. The chops were seasoned and then grilled on the stove top. All chops were cooked to meduim-medium/rare.
I put Scott under a blind test and he picked the grain meat being that with the stronger taste with the sour undertones. The grass fed chop was clearly the more tastier and I found myself wanting to continue sucking on the bone from the grass fed but I had not the same urge with the grain feed chop. I had a friend recently tell me that they usually experience a metalicy livery taste from vacuum packed meat. My theory is that it isnt the vacuum packing more than its probably grain fed meat.
Id be interested in anyone elses feedback.
Cheers