I can't improve on your guess, but I can tell you that Camellia Forest sells Schima superba. I've seen that listed as a variety of S. wallachii on one site but separately on others. If you want to try to key it out:

Here is a link that might be useful: Schima

Thanks Karen - that sounds like a real possibility, esp. given the proximity of Camellia Forest to Plant Delights.

it could be "oleifera" a white hybrid camellia that is winter hardy to zone 6b.

Try this link>

http://www.usna.usda.gov/Newintro/camelli1.html

Just a thought. Lyle

Just got an email message from PDN - it's Schima argentea, so I was close. Thanks, everybody!

I read recently that plant breeders at NC State are crossing that with Franklinia alatamaha with promising results.

Here is a link that might be useful: plant breeding