In the meantime, before starting SockTwo, I moved SockOne from three base needles to four and drove myself crazy for a few rounds trying to figure out how to hold the extra needles with knitting with the fifth. Two days later, I had it, and yes--like the 5-needle version better. However...this means my "free" needle is needed for both projects (OK, since I really can't knit on both simultaneously) as I have one four-needle set and one five-needle set (both US size 5.)
SockTwo is on the left, SockOne on the right, as of the last row knit. The blue needles were inherited from my mother--they're aluminum. The steely looking ones are steel. The yarn is 100% wool, worsted-weight. Both socks were cast on with the long-tail cast-on, on larger needles than they would be worked, and both then had one row of knit stitches into the cast-on row before starting the 2x2 ribbing. When SockTwo catches up with SockOne I'll alternate rows of ribbing until the cuff's the length I want, do one heel flap then the other, then turn the heels one after the other, and so on. The goal is no more than a one day separation between finishing one and the other.