That's a good question and something I've been wondering myself. Although honestly, I'm not as concerned about cleanliness anymore as I am with engine wear. A lot of oils show very good engine wear numbers and might not clean as well, while others might sacrifice engine wear in order to maintain cleanliness (and perhaps to acheive longer drain intervals)
From what I understand, Schaeffer oil does keep engines pretty clean, I believe Bob has some pictures of engines run a long time on the stuff that look pretty awesome inside.
You can always run a cleaner like Neutra or Auto-rx every 50k though, just to be sure.
If the engine is started from the first oil change on schaeffers, it will not only keep it clean but will not allow any varnish build up. I have one guy that has used the 15w40 in his car since first oil change. Had a timing cover leak underwarr. So after pulling the timing cover, oil pan and valve cover the dealer called him and asked what he was using since they have never seen a 36,000 mile motor look like that did, which they stated was like it just came from the factory.
I wish I had gotten pics of that one. To answer your question, yes, it will keep the engine as clean as any "full" synth.