iMac (late 2012) 27" Crippling Wifi Network

[arcendus]

Not only is my new iMac running incredibly slow when connected via WiFi (my Macbook Pro has 0 problems when located in the exact same place as my iMac), but it slows down the entire WiFi network whenever it's connected. I've searched all over the place and found various suggestions that I've tried with no positive results.

If additional details would help diagnose the problem, I'd be happy to provide any information.

Consequently, to make this post I had to sleep my iMac to disconnect it from the network so I could even navigate to this page...

 

[arcendus]

PHY Mode: 802.11a
BSSID: e0:91:f5:b0:d3:19
Channel: 153 (5 GHz)
Security: WPA Personal
RSSI: -70
Transmit Rate: 54

or my second WiFi network,

PHY Mode: 802.11g
BSSID: e0:91:f5:b0:d3:17
Channel: 1 (2.4 GHz)
Security: WPA Personal
RSSI: -59
Transmit Rate: 54

 

[drsox]

PHY Mode: 802.11a
BSSID: e0:91:f5:b0:d3:19
Channel: 153 (5 GHz)
Security: WPA Personal
RSSI: -70
Transmit Rate: 54

or my second WiFi network,

PHY Mode: 802.11g
BSSID: e0:91:f5:b0:d3:17
Channel: 1 (2.4 GHz)
Security: WPA Personal
RSSI: -59
Transmit Rate: 54

Why do you have 2 networks ? What's connected to either ? Do they have different names ?