Note: Haven't flashed this yet, waiting on FKU and first release version.
I keep Wifi on, but use the following. All emails, notifications come in fine, and battery drain on the GNex was great, as is stock N5:
Network notifications - Unchecked
Keep Wifi on during sleep - Always
Scanning always available - Unchecked
Avoid poor connections - Unchecked
WiFi Frequency Band - Auto
WiFi optimization - Checked.
WiFi works great, no crazy drain. So if you do the above (if that setup suits your use case) and still get crazy drain, you may have a problem.