I would Get a HD 7850 or 7870 as it is more than capable of running current generation titles oh high ish settings at 1680x1050 you are only going for 60 fps anyway and it is more or less balanced with your processor.
Also are you sure that you don't have the settings wrong as most games only go to 1680x1050 when they are in 16:10 aspect ratio. When you have a 1920X1080 monitor you want to be running 16:9 aspect ratio.
Here is an example in counter strike source on my 1920x1080 monitor...

Above is in 16:10 mode and below is in 16:9 mode. As you can see in 16:10 mode you can only get up to 1680x1050 but in 16:9 mode you can get up to your native res.

Also are you sure that you don't have the settings wrong as most games only go to 1680x1050 when they are in 16:10 aspect ratio. When you have a 1920X1080 monitor you want to be running 16:9 aspect ratio.
Here is an example in counter strike source on my 1920x1080 monitor...

Above is in 16:10 mode and below is in 16:9 mode. As you can see in 16:10 mode you can only get up to 1680x1050 but in 16:9 mode you can get up to your native res.




















and I think the "max power consumption" on some reviews only state the graphics, not including the rest of the system.
... well yeah, i really focus on the GPU's max power consumption itself coz i know the rest of my system like my cpu needs little power so, yeah... i suppose my psu's good... anyways most manufacturers recommend 500W or higher psu's..