[MENTION=22412]Oak R[/MENTION]
The Nexus 5's support is ending with Android M (6.0), so you'll have to rely on developers to make stable ROMs for Android N and further versions.
It is also a generation older than the G3 (which is SD801, Nexus 5 is SD800).
The G3 comes in two models, Snapdragon 801 and Snapdragon 805.
The former is more common, you can get an American T-Mobile variant (D851) or an international version (D855).
The Snapdragon 805 variant is a Korean version, comes in F460L, F460S and F460K models.
It will definitely get further support, well at least the SD805 version. It will last longer than the Nexus 5 and is a whole year newer.