I do have a distinct impression that rolling resistance is much lower than previous few sets of wheels.

you don't need to quote the above post!

Unfortunately never had the pleasure to ride the 7900 series, shame.
Got the 9000 after a series of recommendations of DA C24 as the best allrounders in this price category,
I wish there was someone adding to this thread who actually tested both.
I do have a distinct impression that rolling resistance is much lower than previous few sets of wheels.

(additional 50km test riding on a route I did 20+ times, I was able to beat most sections,
same conditions, same form, same weather etc and not really pushing it too hard... so I guess this is a promising)

I absolutely love the skewers for firm and easy dismantling of front wheel,
I still have not weighed them - I hope that someone online will)

Let me answer this for you:

1. No the 9000 series is not a lower rolling resistance wheel bearing or any other magic mumbo jumbo compared to 7900 or 7800 wheels.
2. The "feeling" that they roll better is in your head, or more related to rubber and tire pressure than the wheels.
3. You are excited about your new wheels and riding harder. The wheels are NOT faster, but you may be with them.

Your performance improvement is psychologically motivated, not due to improved technology. Nonetheless they are fine wheels.

Does anyone think with the absence of the opti-bal in the C24, make it sort of a flexible wheel? I'm kind of a high power guy and do a lot of climbing. I'm not sure if these wheels will suit me. I'm seeking a nice light, stiff wheel.