Does your G2 getting into download mode or recovery? If it is.. Follow the tutorial and go back to stock. It'll solve the problem. LG G2 Stock Firmware (Go Back to Stock) | LG G2 | XDA Forums
Don't worry about phone number showing as Unknown. Almost all Korean phones show this behavior. But it should show you "UFone" in the Notification Area, when you drop down the Notification Menu from the top.
However, if the SIM is not working then it can either be: 1) SIM is old and should be replaced with a new one. 2) Baseband of the phone is corrupt (in which case NONE of the SIMs will work on it).
I only have experience with MK650s so i don't know how good 690s sound.
I think that 690s only have the Secure Fit kit with it additionally. You know, those different sized caps as per your ear hole size. Rest of the specs of both look exactly the same.
Im sorry yar, i forgot about your VM.
Coming to bios updates, when i updated my laptop's bios i lost a lil battery life and gained nothing.
On the motherboards side, it rectified some problems like the computer wont wake from sleep, auto ocing etc.
So if it is an update u may do it, i dont think there will be any harm in doing so.
And sure the 10400F is a good buy, performance is near identical. But the K model is OC'able for some extra juice. Not sure if that worth anything to anyone.