I had a similar situation in a basement bathroom. Location already had the rough plumbing from way back in the concrete floor and I wanted to avoid moving the toilet a couple of inches in the concrete. So, I ended up ripping 2 x 4's to something a bit smaller than a 2 x 3. My wall was backed up against the foundation so I had support behind them. If you have a free standing wall, and need the room. I'd suggest using 2 x 3's (or even ripping them narrower) and if you want a stiffer wall, go 12" on center. One other thought, when I remodeled my entire house to the studs, I put insulation in all walls. The house is quiet and feels tight. No noise through any wall. Just don't put any vapor barriers. If you really need space counting inches, you could even consider using something like 5/8" T-111 as the wall. I have used that inside primed, sanded and painted. With some minimum framing I think you could get away with it almost free standing.