I just try to keep track of the stats on my current gear and where I sit with that, and then I look at the differences with whatever item I'm looking at in AH and figure out a rough estimate of what I'd gain and what I'd lose.
http://www.spacepiratesandzombies.com/ i7-2600K|MSI Z68A-GD80|1GB GTX 460 x2|8GB DDR3 @1600MHz|Corsair Graphite Series 600T White
It depends how much the rest of your gear increases your Dex. Unless you have fairly high Dex that damage increase probably won't be enough to offset the dex loss.
The difference of 200 DPS with over 1000 in the primary stat is phenomenal. Losing 100-200 Dex to increase your weapon DPS by over 200 is well worth it. Get it with a socket for +Crit Damage if it doesn't have that stat.
Currently writing a guide for: Diablo III Prolific Contributor: www.gamefaqs.com/features/recognition/32351.html