You can, but it will almost certainly get damaged so we strongly advise against. Boat Wakeboards have none of the protective properties of Cable Wakeboards such as a Grind Base or ABS Rails.
This comes down to personal preference. The bigger board will be more stable and the smaller board will be more lively. Personally, we'd tend to go for the bigger of the two boards if you're riding Cable and the smaller if you're riding behind the boat.
We usually suggest going smaller as bindings will stretch a little with use. So, if you're a size 10 and the binding choices are 9-10 and 10-11 we suggest you go for the 9-10.
This video from O'Brien should explain all.