When I was buying my ENVE rims some time ago I was recommend the 3.4, which I purchased. These are lightweight and give you a good mix of aero and climbing ability. Braking on the rims is a little dicey in the wet on fast downhills though, but if you are sensible and get on it early then it’s ok. I have these laced to Chris King Hubs which provide a decent combo. I preferred the ENVE over a fulcrum racing zero wheel for looks and for climbing. A fulcrum racing zero is a bullet proof and cheaper option which will save you a few thousand. You could use this money for other upgrades on your bike, training etc. You will lose a little speed on the flats with this option.
I have never ridden Zipp NSW so cannot comment on how they perform. Both ENVE and Zipp can always be rebuilt. A fulcrum you will just bin when done. Not sure about a dura-ace c24. I believe these can be rebuilt too,