Every 6dB of antenna gain doubles your range, as long as you are on axis. Improved reception in one direction is at the expense of reduced reception n other directions.
Antenna gain specs are like speaker specs. Don't believe everything you read.
The reason I brought this up is that more often than not my setup is in a corner or at the end of a building and I only care about coverage in one direction.
Often my rack is in the same closet as the network equipment and I can connect to their unused jacks and move my router from place to place in the building, but that gets tedious if I'm going back and forth at all, or I have to bring multiple routers. then remember where I left them all.
Also, I'm thinking I might be able to get away with something like an Airport Express for local coverage in all directions and then add a directional (or two) that I can point at the trouble spot(s).
These ubiquiti units (with mimo elements) seem a whole lot more portable than external directional antennas too.
Jason