You did well to get four and a half years out of them with all that riding. I had a pair of Fulcrum Racing 5s. The rims wore through in around 2 years with relatively light (~2500 miles/year) use albeit in all weather.
I've gone back to Mavic Open Pro Ceramic rims which last years but they're not the stiffest so I'd say you need plenty of spokes!
I'd love to find a pair of nice factory built wheels with ceramic coated braking surfaces.