Hehe, well i set the frame counter on in HL2 while playing, and set the screen res to 800x600 and had all the settings on High, with full 6x Antialiasing and 16x Antistropic Filtering, and I was getting 80-120fps...
I then limited using the command console the fps to 70 (my monitor res) and then set the screen res to 1024x768 with same settings... and it still wasn't dropping below 70fps!!!
I prefer the games look at 800x600 though, looks a tad bit sharper which I like the look of.
But yeah, that really shocked me... and I have no idea why its suddenly able to go that high with no slowdown anymore.