Lower res or lower quality?

My monitor's native res is 1920 x 1080, and it is a burden on my two video cards. Which would put less stress on them -- lowering the res in a game like Team Fortress 2 or lowering the overall graphics quality to low while keeping the res?

I need a significant boost in FPS from the 'recommended' graphics settings that TF2 had, which was mostly high settings.

lower res. kill AA if you have it enabled.

give 1680x1050 a spin. lower res/no AA is gonna be a bigger boost then lower graphics quality settings. just because your lowering the settings (IQ), your GPUs are still pushing the pixels to that big res.

1920x1080= 2,073,600 pixels to render
1680x1050= 1,764,000 pixels to render

Drop the res, watch the fps fly.