I never measure each stud separately for simple non-loadbearing interior partitions, unless the height varies by more than an inch. I always purposefully undersize them when nailing wall together on the floor, so I can be absolutely positive that I won't have to pound the crap out of it to stand it up and fit it in place. For these type of walls it doesn't matter if there is a 1/2" - 1" gap between the top plate and the ceiling framing. I just shim in a few spots where I am nailing up through the top plate and done. This method is much faster and easier and it is easier to move the wall around if you change your mind where you want it.