Surface should be raw and good enough

A good way to speed up Blood is to buy a new processor

> Does using the Overlay option speed up Blood, or should I just stay with the surface option?

It's different on every computer so try it.

"Surface should be raw"

What does this mean?

I think he means it's the simplest output. Try also ddraw and OpenGL. You may notice some slight differences depending on the videocard you have.

Is there a DOS based benchmark that can show the speed and/or quality differences between choosing the various output formats?

run the game's demo mode with fixed cycles and compare the host cpu usage, that's how I do it.