but I'm not sure which channels are good or bad to use on 5GHz.
In order of preference,
the indoor-only channels: 36, 40, 44, 48
then the first DFS band: 52, 56, 60, 64
then finally the upper band: 100 - 140 (also used outdoors and WISPs in unlicensed mode).
Observe that in 40MHz mode, "36 + upper" and "40 + lower" are the same pair of bonded channels (and so on),
If in doubt, auto is ok, but if you can check channel usage you can look for a 40MHz gap, but if the other APs are on auto they will move around anyway. It's less of an issue than on 2.4GHz.
prompt $P - Invalid drive specification - Abort, Retry, Fail? $G
prlzx on iDNET: ADSL2+ / 21CN at ~4Mbps / 700kbps with IP4/6