The definitive guide for BF3 tweaking is available online; Guides: Battlefield 3 Tweak Guide - GeForce
This is a good read, especially for those in the market for new video cards. Personally, I'm the type that is not deadset on ensuring that i can absolutely MAX out the settings on a particular game. In fact, I argue that often times the highest quality settings can hardly be noticed and it's simply not necessary to tick every single box to the highest level possible.
Hopefully this guide will give you some perspective on what the settings do, what impact they could have on system and gaming performance and will demonstrate just what level of detail (as miniscule as it might be) that you would be giving up by not running at Ultra, but perhaps high or even medium.