If your question is... is it better to turn down the graphics in order to get better fps online, then the answer is yes. It just depends how good your computer is, if your computer can't handle any higher than medium with good fps then leave it on medium.
BF3 plays smooth above 40FPS, so imo 60FPS is not necessary to have good performance, unlike other online games.
On all online games I choose better fps over better graphics untill I get 60FPS, If I can have 60FPS with all the eye candy too, then thats a brucey bonus, but if I can't then I will lower the graphics to get 60FPS, however, BF3 is my exception to this.
Firstly because BF3 plays well with 40+FPS, it does not need 60FPS to play well imo.
Secondly BF3 is not a "twitch" shooter, so 60FPS is not as important as it is on other shooters.
And thirdly BF3 looks so good on high/ultra I cant settle for anything less.
So in short, my advice is to turn up the graphics as high as you can without lowering your fps below 40, but If you really must have 60fps then lower your graphics untill you get 60fps.
its genrally accepted that you turn down the gfx. but 1s you get to 100 fps there will be no difference at all. as your game will only send a maximum of 100 packets so 1 packet per frame... if your limited to 40 fps then you would benefit from reducing the packets to 40 also... this just syncs up everything and will reduce game lag and make playing smoother over all.
some cheats will use this as an exploit by binding it to a key forcing a lower packet count and creating game lag so they get an advantage... most servers now scan for this and will ban you for it... so set it and leave it... dont set it below 30 or you may get auto kicked for being to low..(as reducing packets makes you harder to hit, but also makes your targets harder to hit)... so its swings and roundabouts...