I haven't been able to measure the 5m yet, but have now sailed 2x...and bought a 4m with it which I was able to try 1x.
Here in the netherlands it is currently around 2-3degrees celcius. sessions are therefore max 2 hours because after that even in a 5-6mm wetsuit with hood and gloves and 6mm boots I am so cold I have to stop.
On the beach: inflation is faster because the V3 has 2 tubes. the struts also feel stiffer.
Compared to the V2, the V3 is a bit more compact and feels a bit softer. The power build-up is therefore slightly less direct as the V2 without windows. I think the windows cause the V3 to feel slightly softer.
The big difference is in the handles: the handles of the V3 are slightly elastic and because they are thin, I can also use them with gloves without armspump. They are really an awesome upgrade!
It feels like I can now sail a bit higher upwind, at least a lot higher than one of my buddies with the Strike V2 who has aprox the same level.
Surf:
The V2 was imo already super in thast, and that is unchanged. The surfhandle could have been a bit wider, because with gloves and numb fingers from the cold I don't always get in properly this way.
Fortunately, with 2 or 3 fingers it is also easy to surf and without gloves no problem. As with the V2, the surf handle is very stiff and allows you to really controll the wing.
Hopefully it will warm up soon and I can feel a bit better what is happening.
some footage a friend made of me: I,m on the white/green Mantis V3