I put drops on my MTB commuter and put a shorter stem on, about an inch shorter. I didn't measure, since I just swapped for a spare I had hanging around. The old stem was fairly long and the new one is medium-long (maybe 4 inches?)

Before I swapped stems, the hoods were a bit far for comfort but the drops were fine. After the swap, I occasionally wish the drops were a bit further but the hoods are more comfortable. I have considered lowering everything a bit, and have plenty of stack (or stem angle flop) to do that with, but have generally been lazy.