Takes longer, but Spell Users rarely get spells off as it is!
Go with individual BAR rolls with individual Armour/Shield columns for each foe.
If wanting to save time, you could divvy up the foes into two groups Leather/Metal and use the same BARs for all members of each group.
It’s risky, though, as a really (un)lucky roll nerfs your encounter for either side.
That said, IT’S RM, babee!