I have enve 45 and 6.7s.. Basically the 6.7s hold speed better especially over 35kph, once spun up you require less effort than the 45s to keep at higher speeds. But you can feel the weight difference up hills. The 6.7s do not climb as easily as the 45s I find too the 45s spin up easier and faster than the 6.7s. Basically both wheels do different things better than the other. Both awesome wheels with the 3.4s atemping to meet the 2 in the middle. On very windy days I totally prefer the 6.7s but then I am 85kgs.
As the others have said.. You have em coming best to make your own observations