I posted awhile back that merely enabling HLSL cut my games's FPS in half. I've discovered that checking "Switch Resolutions to Fit" enabled me to run HLSL @ 100%. Just an FYI for others that might have the same issue Tried a few different profiles posted on this board and no slow downs so far.
Another thing I noticed....and I'm almost afraid to post this cause it might get "fixed" is that on my locked 60Hz LCD, enabling HLSL allows me to play games like Ms.Pacman (60.61Hz) @ 100% frame rate without the need of enabling the "Refresh speed" option. Whether or not this is some trickery on the part of HLSL is unknown.
Update: HLSL had nothing to do with not having to use refreshspeed. Disabling it yields the same results.