You will get a higher top end speed out of the 12t sprocket but sacrifice the torque that you'd have from the 10t. As far as the #35 chain compared to the #40/41 chain I'm not sure about that.
I have a 10t Tav2 and 54t drive sprocket and get speeds of 30+mph.
Here is a spool calculator you can mess with different gearing combos.
http://box.arthizm.com/calculator/