I'm on 4.3.1 on my iPhone 4 32GB which is factory unlocked so I have no need for an unlock.
What is the latest 5.x.x version which I can update to while also having an untethered JB?
Well neither since I'm in Europe.
Found it though.
According to tiniumbrella the device is 3.1 = GSM and 3.2 would be CDMA, as per the ios FW file names.