re: pricing and using 2 bys vs. 5/4... Grading is everything. I'm rebuilding my deck as well. You might find this useful.
Home Depot's Online prices for PT wood 6" decking.
I hunted through all 100 items in their decking pages and pulled out the 6" wide PT decking lumber.
They really mixed up the naming of the different products... many are the same products under multiple descriptions. All cells with the same color are the same sku, but sold under a slightly different name. (Use the SKUs in-store, so you can compare to what they actually stock locally.)
Note in particular the "5/4 PT Lumber" vs. the "5/4 Premium" (same products).
And note the the 2-by "Premium" are less expensive than the "5/4 Premium", but more than the 5/4 Standard.
5/4 x 6 (1" x 5 1/2" actual) is bull nosed for water run off and appearance. 2 x 6 (1 1/2 x 5 1/2" actual) is not bull nosed, it's just slightly rounded over on the edges. the round overs on 2 x 6's are not very consistent because 2 x 6's are meant for framing.