Sam, if annoyance to someone sitting near you is a major factor, as it appears to be, you might, as Dr. Horse's friend might say, "reflect". As has already been mentioned, it would be quite apparent to someone there when using open-backed phones. Although they vary somewhat, when I tested with my SPL meter at about 1"(not precise, but in the ballpark)using a level of about 80dB, which is loud, but not dangerously so, the level from the open back was nearly the same at 1". Of course, it falls greatly with distance, but at about 3' it was around 20dB lower, which is very clearly audible, considering that typical speech is around 60-65dB.
If you're still going to use open-backed phones, I'd suggest the AKG K701s, listing around $500 but available as low as $250. Better bang for the buck comes with the Grado SR60i, for around $65-$70.
