If the 4's (special wheeler made just for specialized), they are between fulcrum 3 & 5, then the ultegra wheels are probably not a weight upgrade at all.

Hubs and over all build quality MIGHT be a tad better on the ultegra, and they MIGHT last longer. Maybe...

The ultegras are probably a bit more narrow, which in 2017, is not the direction most people want to go. (Most new fulcrum racing wheels are 17mm internal...ultegra is 15).