GPU vs 1080p?

So I have been looking for a new GPU to get for my rig. I currently have a Radeon HD 7850 2GB. It's decent but I can't get above 30-40 FPS on Battlefield 3 on some of the larger maps regaurdless of Low-Med-Hgh-Ultra. I was looking into the R9 290X but then I heard that the card is meant for gaming above 1080P and it wouldn't perform as well as it could with resolutions way above 1080P.

So I am just curious guys tell me what you think! I was wanting something that can handle the games we have now and future games like Far Cry 4, Watch Dogs and The Division.

My monitor is 1600x900 20 Inch with 16GB of RAM, 700W Power Supply.

One card I looked at before I saw the R9 290X was the 7970 GHz Edition. Just tell me what you think guys. I don't want to speed $500+ on a card that wouldn't perform as well on my resolution that it would on high resolutions. Down the road I will probably get a bigger monitor. But for now I have a nice one.

On the other hand is it really going to hit me performance wise with an R9 290X on a 1600x900 Res?

Thanks