The backplates are to help support some of the big coolers different brands use. So if it has a stock cooler then it probably wouldn't have a backplate.
And yes, you will benefit from the 980, especially if you are gaming at 1440p. I have a very similar setup, just throw in a few SSDs and its the same.
I have the Gigabyte G1 GTX980 with the triple fan setup. I do just fine at 1440p, at 1080p it would be overkill, at 4k you would need at least a 980ti, if not 2.