i have no idea if either of these suggestions is necessary, but reducing a 2x4 to 2x3 has a SERIOUS effect on the strength of the stud. for ex, i was given these numbers by a guy who teaches building science at a small university: "A single SPF#2 9' 2x4 that's restrained laterally by sheathing or blocking can support 1820 lbs and a similar 2x6 can support 7061 lbs without buckling." thus, i'd be real careful replacing a 2x4 w/a 2x3 if the wall is load bearing. i THINK, and this is only a "think," you will have a stronger member if you nail your 2x3's into L's; better yet, U's. i have no idea if either is necessary, but reducing a 2x4 to 2x3 has SERIOUS consequences for the strength of the stud. i don't know the exact exponent, but the "strength" of a stud, be that bending or holding load w/ out failing, is not linear.