The primary difference between the 2 BR's is in the size of the villa. 2 BR deluxes range from 1180-1257 sq ft; 2 BR Presidentials are 1250 sq ft.
The occupancy of the 2 BR deluxe is 8/6 and the info says the sleeping arrangements "vary." I believe that means some have K,Q and others have K, 2 DB.
The unit information on the 2 BR Presidential says it only sleeps 4, but looking at the floor plan, that appears to be an error. The info says K,Q, but the floor plan shows K, 2 BR with a sofa bed, which would be 8.
The furnishings in the Presidential units are also considerably upgraded. If you look at the Bonnet Creek photo thread, you may be able to see differences.
The occupancy of the 4 BR Presidential is 12, and two 2 BRs would hold a max of 16, so that may be a consideration depending on the size and makeup of your group.
Personally, I wouldn't max the occupancy on any timeshare unit. 8 people may fit okay into 4 beds, but they're not going to fit so well into two bathrooms!
You might want to call the resort directly with any questions. Their number is 407-238-3500.