Have not read everything, as a bunch of guys here are full of k@rk.
I have an I3 - 8 gigs of ram, and a 9600GT.....running on windows 7....AND A 40" screen
( Yes i know.....a 9600 from the dinosaur age )
My PERSONAL EXPERIENCE, the I3 works just fine. I have no lag, this includes larger maps....
These guys saying an I3 will not suffice.....clearly have not used an I3.
IN SHORT - YES, THE I5 IS FASTER, but....the I3 is plenty powerful enough to run BF3.
If you on a tight budget, dont let these guys con you into spending more money than you have,
the I3 is a sweet processor ( the last of the i3's) and from person exp., with the right card and enough ram,
she will run like a beaut.
If you got cash to spend tho, go for the i5, or, maybe just save up a little more and make all the i5 guys drool by getting an i7
Then you can come back here and talk about how rubbish the i5 is