eh? i've always thought the g-sync is connected to the monitor/screen itself, so it would be unnecessary if i connect the laptop to my own external monitor. like if i already have a g-sync monitor, then there's no reason that i should buy the g-sync version of the laptop as the monitor i'd be using already has it

My understanding is that G-Sync needs to be supported on both sides (i.e. GPU and display). However, it could be that the G-Sync version of the laptop is specifically the display and that external display ports support G-Sync regardless of the version of the laptop and that whether or not it's the G-Sync version only refers to the built-in display.

That said, my comment about it being a 1070 and the need for future support will (I think) still apply. I'd therefore still recommend the extra $100 for G-Sync.