It depends on the layout of your kitchen...what's around the island and where.

5' of clear counterspace is 60"...a very nice run of space!

Speaking strictly about counterspace, if your DH is going to be using it the most, then I would do what he's asked. If it were me, I would also want some space on both sides of the prep sink for the same reasons your DH does. If you were short on space, I might say otherwise, but you're really not!

So, what's around the island and near the prep sink?

My whole island is only 4x5'! :-)

For me, the placement would also depend on whether the adjacent side of the island might be usable workspace or a good spot for others to use the sink. We have ours on the corner of our island because one side faces the stove and one side is our baking workspace facing our baking center...So it's useful for both sides with the faucet placed diagonally/on the corner so that it feels like the front of the sink no matter from which side you approach it. Also, the baking side of the island is where people enter the kitchen and might be able to wash hands, fill the pets' water dishes, etc...all without getting in the cooking work area.

I definitely think a good surface on both sides of the sink is best. We have a 108-inch island that has 28 inches, then the sink, then 64 inches of space. The 64 inches is PLENTY of space and, if anything, I would like a little more on the other side. We have a trash/recycling pull-out under the shorter counter which allows the person at the prep sink to stand in front of the sink, easily reach items on either side and have a trash can available without having to move out of the way.