I can confirm that it runs fine on a 3.2GHz C2D. It is a legit Conroe with 4MB L2, dunno how it would do on one of the castrated models.
I tested it a few days ago on a wolfdale with 2mb l2, it's not to bad, I even tested at 2.7GHz, although I didn't run fraps or anything like that all I can say is that it was playable,
at 3.7GHz I played for a few minutes and the lowest I saw was 33, almost all the time over 40fps going as high as 50-60 in some parts, that was with a HD5750 on 1280x1024 full screen and medium,
but the problem is, the game crashes (game freezes, but the OS still works well, the game process keep working at 90%+ CPU usage and all...), and have some visual artifacts here and there (I made sure to test the system stability, running at 2.7GHz was one of tests as I tested different ram, 3 or 4 drivers, underclocked the VGA, tested it on burntest and other games and it's working stable), which are worse with the BF3 optimized drivers, with the 11.9 it reduces this problem considerably I think, although performance is slightly worse
CPU usage is always around 100%, system memory usage was around 2.4GB, GPU usage is also very high,
I will try to test on low details and 1024x768 later to reduce the GPU impact and see what happens,
edit: just did some quick testing, using catalyst 10.9 now and fraps,
640x480 low was mostly around 40-50fps, lowest I saw was into the 30s just for a very brief moment, I tested it in the first part of the map and then the first part of the subway (I'm not considering the first few seconds of gameplay when it was still being loaded from the hard drive an such),
just slightly better than on 1280x1024 medium,
so it's quite playable on a e5400 at 3.7GHz ("Core 2 duo" with 2mb l2) and DDR2 800 cas 6, but a quad core could easily improve this (Phenom II X4 at 3ghz should be more than enough for a very high quality gameplay), on the other hand the game is much more GPU intensive, but the HD5750 is enough for playing in medium settings in lower resolutions (I think 1600x900 should still be OK),