Adding to what @JacekJ has said, I've used the staged upgrades many times on stacks, but only on more recent firmware versions that 11.x, however I cannot see why it would make a difference.  I would also urge only splitting out stacks from each other, rather than separating members of one stack into different upgrade windows.  I tried the latter a few times and one time (14.31 -> 14.32 for a stack of three MS355-48Xs) the middle switch just went orange and needed the power leads pulled to recover...  Otherwise it has always worked out perfectly. ... View more