I've had occasion lately to notice 2 sets in 'copper'.
Infinity Gauntlet seems to sell pretty well as a set 1-6, maybe better than breaking out individual copies. NM ish sets have been going around $70, which seems a bit better than individual issues. Don't know the time/$ re: moving individual issues.
MSHSW 1-12 also sell pretty well as sets. Recent prices range about $60 - 110 (probably graded in the Fine range at the low price, and saw a 7.0 set sell around $70, and a few "NM" sets ranging from 70 to 110). Probably if the #8 is sold separately, the lot of 1-7, 9-12 would sell slower w/o the key, which might mean you need to sell a bit lower to move it.
I've seen the bronze Marvel Presents 3-12 sets range from $30 to 60, depending somewhat on grades. I'd guess w/o the #3 it's a pretty lame set and would be slow mover, although maybe like the #8 in MSHSW, the key issue alone is worth half the set price.