At that rate you could run dangerously low on oil before an oil change. I'd accept nothing more than a 1 quart add per oil change if doing 3K mile oil changes and maybe 2 over 7.5K miles. Anything more is way too much, and probably indicative of bad valve stem oil seals, or in extreme, bad ring sealing.

My '93 600SL uses 1.25 quarts over 7.5K miles, just so you know where I'm at, and that's at 82.5K miles.