I started a thread asking for the hardware difference between Razr version.. Link
Since nobody reply, I'm still not sure what is the diff between them..
for sure Razr uses the Ti WiLink7 chip.. that suppose to support Dual band WiFi+BT 4.0+FM+GPS..
If all of these device is using the same chip, then the diff might be the wifi firmware..
Update : It turns out that the xt912 tiwlan.ini that disable the 5Ghz band.
So I think maybe by using my Razr wifi firmware & configuration, the 5Ghz band might be enable on your device..
Update : Working on some Razr
Attached is the wifi firmware (Rev 184.108.40.2060.5419) & configuration for dualband wifi
This file is extracted from motorola RAZR Global sourceforge.net page.. Link
the fw_wlan1281.bin is a few kByte diff from the one used in xt912.
you might need to tweak tiwlan.ini to suite your country wifi regulatory
Updated: This is only for GB