Stud wall screws

I'm putting up a stud wall in my attic using 2 x 4's. I plan to use screws instead of nails, what size screws should I use?
Thanks
Dennis

2.5 to 3"

If screwing through the plate into the stud #9-3 1/8"
If screwing to the side #8-2 3/4"
I would use these http://www.grkfasteners.com/en/R4_1_2_information.htm

I would use a deck type screw (stay away from drywall screws, they can be quite weak) at least as long as the typical framing nail used for this application. That would normaly be a 16d nail which is 3 1/2" long. I'm not in the habit of recommending screws for framing over nails at all because although screws have a much better holding force due to torque they are also much more brittle because they are typically harder steel and therefore don't have near the sheer strength of a nail. In the case of a stud partition wall you're not going to be overly concerned with sheer so screws should work fine.