770 & Samsung 840 250GB or a 780

I would not agree that the gaming experience will improve as it would not impact frame rate or quality. Only loading times within the games would be much quicker. In my experience the biggest impact I've seen in work under the operating system, all software start up, multi application work, and work on software heavy on fragmented cache (example. Lightroom, lots of pictures).
Definitely SSD is worth buying/must have for OS for the comfort however if you are using your PC mainly for games I would prefer better GPU + small SSD.

@Laminator Nice card and good choice IMO