There are typically 15-20 clients connected to that Netgear router during the day, including several mobile phones. The clients are not all continuously active though. The ones in my lab are idling in Windows most of the time.
I used the "Site Survey" feature of 868L to take a signal strength reading of the router 5GHz signals in my lab where the D-Link bridges are located. The ch 36 signal is in the -63dBm ballpark, and the ch 153 signal is around -51dBm. Not the strongest of signals, but considering there are 2 walls separating the NG router and my D-Link bridges, it's not too bad. I also used inSSIDer Lite to gauge co-channel interference and overlapped channels.
Today I also changed the Netgear router 5GHz-1 radio from ch 44 to 36, and switched one of the two 868L bridges to connect to ch 153 instead of ch 36. Will see if there is any change in wireless link drop behavior. There has been no link loss observed from any of the three D-Link bridges since last Friday. Not sure what led to the better behavior, though.