Are you on current firmware? I think in R66-R68, the 2.4GHz WiFi drivers were stuck in 20MHz channel width, but that shouldn't affect 5GHz.
Interference could be at play. I have a neighbor using wide channels on an old-firmware NetGear router, and it clobbers everything 2.4GHz in my house (bluetooth, WiFi, had to move to 5GHz cordless phones, etc.) In theory, it should affect all routers, but if the other router is locked to a set channel, and under heavy use, the Almond+ might be stuck using something less than ideal.
Can you try using iperf or netperf between two laptops?
What about between the A+ and a laptop? OpenWRT has netperf, so it should be available if not already there.
Can you test the router in a different building, or at least several tens of meters away, maybe on a different floor?