5.5 is going to be an incremental step down from Fulcrum 5's which btw are very good training wheels...I have two sets and love them.
the .5 is a slight deviation from the factory 5's...either different hub, rim or spokes...likely spec'ed by Cervelo.
Fulcrum makes wheels expressly for the OE bike makers which is a slight deviation from their factory wheels which btw are made by Campy.
Will it matter much? No, probably not.