I find the NEXX carbon very comfortable to wear. Stable at high speed a little shakey during head check, I made the mistake of going to the quick disconnects for the face sheild which ruins the seal so you get gaps between the seal and the sheild and the adjustments won't seal it tight enough. Going back to the old screw in face sheild. Very very light helmet, lighter than the Cosair RC by a literally a hair but the Cosair RC carbon feels much lighter because the weight is distributed around your head evenly and more stable (no wind buffeting) where the NEXX is a little heavy in the rear and buffets a little more. I don't particularly like that the Nexx neck roll is non removable. The NEXX has Outstanding air flow 3/4 to full up right position.
The Cosair V Race Carbon is a thing of beauty! Its really like a peice of art. Very very light. Like all the Cosair V it's the most stable helmet at speeds and during head checks and IMHO the race carbon seems to be more stable due to the light weight and is less stressful on the neck. Excellent air flow in the 3/4 to the up right position and massive air flow in the tuck position like all Cosair V's. Quiet in the tuck and average noise in the up right position. What impresses me the most is how stiff the opening of the shell is. Its just like the regular Cosair V, you could stand on it and it won't break. Where the NEXX is not that stiff I would be a little scared to stand on it. All the pads are removable including neck roll.
Is it worth $4K for a 1/2 lbs lighter helmet? I my most honest opinion:
1) "Only if you have that kind of cash to throw around" otherwise the regular Cosair V will protect you just as much.
2) 1/2 is actually a lot to hold up at high speeds if you are a track enthusiast you will notice the difference on the neck. I did. The NEXX is also light but not as stable as any Cosair V so it seems a little heavier than the Cosair V RC.
3) if you want a rare helmet and the people you ride with most likely won't have one.
To me it's like owning a Ducati you pay thousands of $ more than a Japanese bike for a few tenths of a second faster? No, it's because it's exotic and rare compared to other bikes.