I don't think the different crossing patterns have anything to do with it. In general you want the maximum possible number of crossings on a rear wheel to make the spoking as near to tangential as possible. People will use fewer crosses on non-drive-side spokes, I think the idea is that since they are under so much less tension than drive-side, they don't transmit as much torque. (Hm...I have to think about that one....)
More crosses put less strain on the hub flange, but I think most hubs nowadays are approved for radial spoking. I've never seen a hub flange failure, but I've seen plenty of rim failures.
With a light aluminum rim, I would want 32 spokes for the rear.
at 150 you'll be fine haha... Check out the clyde section for those (us) wheelbenders. I have been crossing all season on Fulcrum racing 7's. I roll about 220# minus bike. Rear is 24 spoke, and i have hit some nasty ruts and holes with these wheels on and off road, with no problems
Are you worried about them breaking? 150 lbs with 32/28 should be more than enough strength. it's a pretty common setup. Open pros are super solid rims. Plus, cross tires are run at a substantially less psi which means the tires will soak up a lot of the rough stuff.
2005 Fuji Cross Pro, 2006 Allez Sport, Mid 70's French Bike named 'Pierre'
I am currently riding (because I am lazy and don't feel like fixing the "race" wheels) a 32h Ultegra/Open Pro in the back and a 32h(I think) Mavic wheel that is really gosh darn old and has that funky star shaped plastic looking hub flange with straight pull spokes that predates the Ksyrium. I rode these on 3 short track mtb races on my cross bike and a cross race this Sunday. I bought the set for a whopping $80 on craigslist.
Did I mention that I weigh 220lbs and most of it (not all by any means) isn't fat. In other words, while I don't have a Powertap, I think I do OK in the torque/watts department. You are a measly 150 lbs. I eat that much for lunch and breakfast put together.
If you are actually still reading: YES, those wheels are strong enough. Unless you are planning on riding off of cliffs.
Flargle: Is an Open Pro considered a light weight aluminum rim?