You don't need a chart if you know what overlaps. The netsh cmd I provided indeed does show signal strength. Here's a piece of sample output where you can clearly see, in % the signal strength:
SSID 13 :
Network type : Infrastructure
Authentication : WPA2-Personal
Encryption : CCMP
BSSID 1 : c0:7c:d1:9c:0a:29
Signal : 38%
Radio type : 802.11n
Channel : 11
Basic rates (Mbps) : 1 2 5.5 6 11 12 24
Other rates (Mbps) : 9 18 36 48 54
BSSID 2 : 92:0d:cb:26:d0:90
Signal : 36%
Radio type : 802.11n
Channel : 11
Basic rates (Mbps) : 1 2 5.5 6 11 12 24
Other rates (Mbps) : 9 18 36 48 54
BSSID 3 : 02:ac:e0:f9:b9:60
Signal : 28%
Radio type : 802.11n
Channel : 11
Basic rates (Mbps) : 1 2 5.5 6 11 12 24
Other rates (Mbps) : 9 18 36 48 54
SSID 14 :
Network type : Infrastructure
Authentication : WPA2-Personal
Encryption : CCMP
BSSID 1 : 5a:23:8c:39:de:06
Signal : 22%
Radio type : 802.11n
Channel : 11
Basic rates (Mbps) : 1 2 5.5 6 11 12 24
Other rates (Mbps) : 9 18 36 48 54
I'm well aware of channels above 11 not being available in North America, as well as the differences in the 5GHz range. I do not believe people need to spend money to determine their wifi environment. You feel differently. That's life.