Overall G-Sync is overpriced, monitors that support it cost more than $100 more, so I think it isn't worth it.
Take $800 for GPU and monitor.
You get a monitor for $400 and a GPU for $400.
That is a 970 or a R9 390.
You get your monitor for $300, that leaves $500 for GPU.
That is a GTX980 or R9 Fury.