Hey all, I'm not a Verizon user but I've been having this same issue with my own ISP and cable modem / wifi router setup and think I finally found the bottleneck. It seems to be TKIP encryption primarily, but also could be WPA-PSK in combination as well. I too am paying for 50mbps and was only getting 20mbps on my wifi but near 50mbps on my wired.
I have a ZOOM 5350 cable modem (w/ built-in wifi) but the wifi signal wasn't great. I decided to buy a Medialink 300N wifi router and make that the dedicated access point and disable the ZOOM wifi. To my dismay, it didn't make much difference... so I knew it had to be something in the router settings.
Long story short, I found the perfect combo of settings that made a world of difference for me... I have now jumped from 20mbps to 30-40mbps on wifi:
Network Mode: 11b/g/n Mixed Mode
Channel: 11
Bandwidth: 20 MHz
Security Mode: WPA2-PSK (<-- only! Not WPA or WPA/WPA2 Mixed, etc.)
WPA Encryption: AES (<-- only! Not TKIP or TKIP+AES mixed)
I tried these settings on both the Medialink signal and my original ZOOM modem signal and it yielded improvements to both, so I know these are proper settings that make a difference. Although I must say the Medialink 300N is still a better wifi signal than my ZOOM modem has because it's yielding more mbps improvement than the ZOOM signal.
In conclusion, it helps to have a dedicated wifi router (the built-in w/ modems don't usually seem to be as good), but also don't expect you will ever be hitting the full 50mbps bandwidth on wifi either... it just ain't gonna happen. Wired connections FTW on speed, but try these settings and hopefully it will maximize your wifi at least.
Good luck!