I don't see any reason to go any lower than 1680. However, I'd recommend the 1920 for future proofing. You can still select a lower full screen resolution back down to 1680 should you choose to without too much artifacting. But you can't watch full 1080p on the 1680.
Besides, when you update that machine, you'd be kicking yourself later if you went 1680. Future proofing FTW.