Download speed with Ethernet vs WiFi

[Kody_Reef]

I've got an Arris SVG2482AC cable modem and switched to a 600 Mbps download speed. When connected via ethernet, I get a 600+ Mbps download speed using either speedtest.net or speedtest.xfinity.com. But, when connected via WiFi (using a USB Linksys WUSB6100M for WiFi adapter), I get not more than 250'ish Mbps download speed. Same deal with a laptop and using an iPad to test download test. Is there any configuraiton tweaks that I need to configure is it a WiFi limitation with my cable modem.

[EG]

FWIW, Wifi speeds will never be the same compared to hardwired speeds. There are just too many variables / limitations. You can Google for more info.

[Kody_Reef]

"FWIW, Wifi speeds will neverbe the same compared to hardwired speeds. There are just too many variables / limitations" 

This is a given - no need for googling. What I'm trying to figure out is why is there a big descrepency. I've got the Arris SVG2482AC within 15 feet from my desktop. No variables/limitation that may interefere with the signal. I was hoping that there might be settings on my old Arris that can be tweaked. I've checked Arris site for any firmware - there weren't any.