Hello.
My last monitor was a 22 inch and i played SHIII with HiResFix in 1680x1050 without problems except the little stretching.
After i buy a new gfx card and a 24 inch monitor i edited the d3d9.cfg file to 1920x1200 and get the error message "can not initialize 3d engine". The monitor was connected via dvi cable. After buying a "Dual DVI Cable" no more problems. Some of my friends have less problems with gaming graphics after this tip (hint?) and changed their hdmi cable to a dual dvi cable. Now i am playing SHIII in 1920x1200 and enjoying it.
Maybe this helps and sry for the poor english.
Greets from Germany. Echol

t.
PS When i put the d3d9.dll and d3d9.ini from Widescreen MaGui into my SHIII directory and set the ini file to 1920x1200 i can't play the game but can make great screenshots (1920x1200).