Having been playing with this spec for a while now, I've had a close look into most of what's been brought up.
Combat Potency does proc off sword spec attacks, even though the attack itself takes its damage from the main hand. This will no longer be possible in the patch though, as sword spec attacks will be changed to 'real' white main hand attacks.
Sword Spec *does* take its crit chance from your main hand fist, and so it gets the 5% bonus crit chance. I've pretty well confirmed this just through merging all the data in my SW Stats' time line and comparing crit rates between Sword Spec, normal attacks and sinister strike. This is something that wont change in the patch.
And as for DPS, this is probably the cleanest example I could find at such short notice:
http://www.lossendil.com/wws/?report...=5104-5390&a=6
Taken from the night before we downed Morogrim for the first time. You can see fairly easily where sword spec takes its crit chance from, and where it takes its damage from (Main hand for both).
Myself and the top dagger rogue have roughly the same gear, and we tend to have fairly equal DPS on most fights, so there is certainly nothing lacking damage-wise.
The only problem I have with it, and its the reason I'm probably changing to pure swords as soon as the new arena season comes out, is that I think having the chance to proc an extra attack with your main hand is just plain old better than extra chance to crit with it, especially given sword spec will likely be able to chain proc come the patch (Will test this).