That sort of testing is definitely on the agenda for this weekend. The extra zoom reach is nice but not terribly critical as I do have other lenses which cover that narrow slice of spectrum.
Originally posted by ZombieArmy What the mount is made of means absolutely nothing, it just makes the product "feel" more premium.
That being said, unless you need the extra 10mm, the Sigma being better at close focus stuff seems to make it a clear winner.
I would however do some controlled tests on a tripod and do some pixel peeping.