Think you have them the wrong way around. Dont get a poor monitor out of fear that your GPU couldn't handle a high end one, 1080p 45fps will look the same on a 1440p 120hz monitor as it will on a 1080p 60hz monitor (due to scaling it wont completely, but close enough).
Anyway, the 780 is still a fairly powerful card, equivalent to a 970 if I remember correctly. The ROG Swift is a fairly high end monitor and one of the few ways you could find a 780 lacking, but I wouldn't get a lesser monitor because of the GPU. The monitor will outlast whatever GPU its hooked up too, get a good one.