I bought my Lumia 920 in December 2012. Until now, my lumia 920 has got 3 firmware updates (1242 to 1249, 1249 to 1308, 1308 to 1314). I am not sure about HTC 8x.
Also the battery is slightly bigger on Lumia 920 (1800 mAh vs 2000 mAh).
In my experience, you have to add your main Microsoft account to your phone again. However, you can't do that if you do not reset factory the phone. I reset factory to get my Lumia 920 back into my Microsoft account.
I recommend that all unused phones should be removed from Microsoft account...
This firmware and manufacturer got a 4G option. This is Thai firmware.
Firmware revision number: 1232.5962.1314.0002
Manufacturer name: RM-821_apac_thailand_319
I purchase my Lumia 920 in Thailand and it is unbranded.
I use Nokia Software Updater for Retail 3.0.4 to upgrade to 1314 last night.
Firmware revision number (about): 1232.5962.1314.0002
These are my Lumia 920 information (extras+info).
Manufacturer name: RM-821_apac_thailand_319
Mobil Operator...