The base $849 model of the y510 only has the 720p screen. The GT 750M should be ok for gaming at that resolution with low/medium settings. It will not perform well at any resolution higher than that. The base y410 doesn't give you much else over the 510 with the exception of a tiny bit of extra GPU horsepower.
Yes the y510p is good for gaming. The difference in the two I believe is there screen resolution. Which if you find the 1080p on your laptop to high to game with without it lagging you can always adjust it. Plus it will have a clearer picture when watching video.
The base $849 model of the y510 only has the 720p screen. The GT 750M should be ok for gaming at that resolution with low/medium settings. It will not perform well at any resolution higher than that. The base y410 doesn't give you much else over the 510 with the exception of a tiny bit of extra GPU horsepower.