RCurtiss -
Both you, and your Dad, will have a great time at the 5th Major. The event is a blast, and the camaraderie even more so. As to playability, the White course is quite fair. Like most courses, should the wind really pick up, "daily par" can go from 72 to 80, for everyone. You won't play better surfaces, the greens are terrific, and Dismal (White/Nicklaus) allows/rewards creativity far more than most.
As to your original post, I think you asked about the "gulf" in ratings between Sand Hills and Dismal (White). First, Sand Hills is truly wonderful and deserves every accolade it receives. On the surface, to me, Dismal (White) is pretty severely underrated. Mind you, its a great neighborhood, and the White does seem to suffer from this. By definition, every course falls short of #1, but I've never seen a really good course placed so far from a highly rated neighbor. In my own (fairly well traveled) world, I would place the White course in the top mid 30ish (Modern) range. Much closer, yet still well behind, Sand Hills. I also think it probablyt proper to throw out earlier ratings - both the course and irrigation have been changed for the better...it isn't the same course as it was at opening, not even close. Time and some simple changes have been kind to the White.
The new Dismal (Red/Doak) is very special...18 really good holes and not a weak one in the routing. I can't tell you where it will be (or if it will be) ranked, but I can tell you it will be fun, natural, and stunningly gorgeous. I've never seen anything like it, and that is a tribute to Tom Doak and his bunch, and great site.
Very much looking forward to meeting both you and your Dad.