We used to do that in CS and Quake III competitions, 640x480, huge targets, easier to spot. But this is different.
What's the use of getting a 80K gaming rig and playing MP at lowest settings when all the pretty scenery and vehicles are in MP? What you said holds good for competitive matches, where you want bigger targets in lower resolution, and the smoothest gameplay. BF3 is meant to be enjoyed in high definition. I would rather have 10 kills less and have a pretty looking game, that's what we all bought our gaming rigs for.