I saw Act of Valor digitally projected and it looked decent but there were some points that it looked a little video-ie. A decently hacked GH1/GH2 in B&W would blow that image out of the water.

In fact pretty much any digital HD cam would make a decent flick in B&W. A old Flip HD in B&W would look as good or better than Clerks. You could emulate a lot of the Pi look in post.

I also just re-watched Sin City in 1080p and that B&W is so clean and clear it looked spectacular.

If you want a grittier look you can do what the guy in that thread did, he showed that in ETC with dynamic B&W film setting, it gives a look similar to 16mm B&W. I think B&W looks best the grittier and grainy save for Sin City, but they gave that film a gritty edge with the effects and lighting.

http://vimeo.com/groups/bwinhd

The digital intermediate for that film was 2K, should be plenty.. 4K is cool, but still overkill for most things.