Turning down the graphics settings reduces the GPU load and your CPU gets more influential to your fps, that's nothing new.
I'm not going to play Crysis 3 at anything but max details with a 3770K + GTX Titan, that's my choice & scenario, and in my scenario we both know that what my chart shows is true and right.
Turning the game settings down will change things ( how much ? depends on the settings & the downgrading level ).
But you can't invalidate results with that argument.
Alt-tabbing out of the game isn't a good idea, sorry, most games do not like that and you'll get inconsistent results even at the very same system clocks & settings.
The 2600K stops scaling there simply due to its IPC, architecture in general and the GPU bottleneck.
As long as we don't have low level access to BF3's engine, we can't tell where the Ivy Bridge increased perf. increase comes from ( could be anything, more efficiency in the Physics calc. thread, etc etc ).
If you're an "eye candy gamer" with a high-end system, you usually game at max details ( in-game ) and AA/TrAA/AF usually, and in that case it is totally indisputable that regardless if you're gunning with a 4.5GHz 3770K or a 4.7GHz 4770K, you'll have the very same performance at high resolutions & maxed game settings ( *maybe some RPG/strategy/mmo games could be an exception, don't know, I said I can't play these kinds of games ).
You can see a plethora of games tested just like BF3 in the chart above
here