Just got a new 27" BenQ GL2750HM monitor. Quick testing on Windows gave 50 to 82 Hz but higher end of resolutions may give out of range messages. 320x200@50 Hz is the lowest I tried - pretty bad looking when scaled to 1920x1080...
Was 320x200 at 15khz? Usually PC's output that mode at 31khz and double each line.
Big tv's make old computers look really bad, because you're supposed to use a 14 inch crt.