Jim,
OAP is much more beautiful than NAP in my opinion. I've taken both multiple times and every time I've been to NAP, I've always thought how much better OAP is. You can always fill up at the last lake before heading up OAP, drop the water off at the top, head to the summit and then come back for everything.
I've never done Whitney from Langley, but have a friend who did it cross country in a day...it was hard. :-)
Permits:
http://www.recreation.gov/entranceDetails.do
