IMHO, which may be wrong, LCD's don't have refresh rates, only response times. THe backlight on the LCD is ALWAYS on. It's not refreshing. If you take a camcorder and look at an LCD screen, you would not see the screen scrolling like you would on a CRT.
So I would say that on LCDs, the more RESPONSE TIME the better. I turn on Vsync to prevent tearing also.
Your 1900XTX should be able to handle the LCD at 75Hz and Vsync just fine. Especially since your monitor can only do 1280x1024.