I use 1680x1050 rez with little problems. The mouse does scroll off screen but thats a small issue for me. Some minor stretching on the screen, hardly noticible.
I'm using a LG L204WT 20.1. Not as nice as yours sik1977
You may need to turn off flat panel scaling in your ati program. I use NVidia. Then set your screen rez to default. In your d3d9.cfg file change the rez accordingly to match your default screen resolution.
Personally your flat screen is too uber for this game. Talk about overkill lol.
But I would do the same if I was in your shoes so I shouldn't talk.