I come from the Flux V1 5.7 (4,3 and 3.6 also) and have two sessions on the 5.5 Ultra X V2 on flatwater now.
The Ultra X has definitely more power and is more direct than the V1, i felt like the V2 5.5 had a better lowend than the V1 5.7.
On the first session with the rec. 7 PSI in the Fronttube i found it almost too direct in the upper windrange (94 kg, no harness). With 6 PSI on the second session i liked it a lot more, there was more flex and forgivenes in it.
Handling is outstanding, the 5.5 weighs less than my 4.3 Flow. Tacking is the same like with the V1, at least for me.
Btw. for all the riders seeking a wavewing in the Flux V2 i'd highly recommend trying the Flow.
The V2 seems more freeride/freerace, as Jeroen mentioned above, i haven't tried it in the surf, but i guess the weight will help there a lot too.
The guys at MACkiteboarding also seemed to like the Flux Ultra X in the surf.
?feature=shared