This tend to drop the speed for all users. Here's my preferred setup for range extension without the headaches and recalls for extenders. Picture follows.

Testing at peak hours is not a good test. You are testing how much he can eek out during peek and not what he'll get when there are less users. So I have to write that's just a a test of that scenario and not a good test at all unless you want to prove you need a second WAP.

Not to duplicate the classroom but WiFi is shared space and takes all players to cooperate. If one WiFi device breaks a rule and gets piggy, well game over. Or if, and this is a nasty thing to do, set a machine to 802.11b and tank WiFi speed as the WAP downshifts to send a rather long (in time) packet. For this reason I always disable 802.11b and may elect to move to all 802.11n or 802.11ac only setups.