Here's a story from Tom's Hardware. You can read the entire thing if you want to start from sand. :-)
Or you can skip to the page which discusses binning here.
I always expected the processors picked for the "S" versions were basically the same as the non-S versions but tested at a higher quality level. They could be guaranteed to fully function at the S specifications at lower voltages; i.e. slightly better silicon. Lowering the voltage wouldn't be...
I'm sure that would handle a 95W cpu but it's not exactly "low profile" :D It fills up the entire case and cools the entire motherboard. ! You can also get a 300W psu to put in the SG05 so it could certainly handle a quad core as long as it didn't need more than the single 12 volt P4 for cpu...
Here is the official list. 95W quads are listed but it'll be hard to find a low profile cooler that works with over 65 watts for the mini-ITX cases.
http://www.zotacusa.com/forum/index.php?showtopic=975