5cm will be better in chop and better on wave and better on hard landings.

But it will be more power hungry. Being power hungry becomes a problem bellow 18 knots. Above 18 your powered enough any way. Bellow 18 it will depend on your kite selection whether you have fun or not.

40cm is more normal. It will be slightly better at the low end and slightly worse with the above factors.

So,,,... whats your average winds? if its sub 18 get the 40cm if its +18 get the 50cm.

I would stick with the 4cm rocker.
As you said you have only been kiting for one year and often in winds 15-16knots.
Being a relative beginner and your technique probably not yet finely honed you will want to keep as much bottom end as possible.
Once you are pulling large wake style tricks where the landing cushion becomes an advantage perhaps think about more rocker.
Regarding chop I doubt there is a huge difference in ride feel with 1cm extra rocker .

Sorry for my late reply I was in Cyprus for vacations where I got some good kite sessions in choppy conditions. My feet paws actually started to hurt after a while and I was blaming my currents board stiffness and bad foot straps.

One thing that really really annoyed me is that as I go upwind my board tends to dive into the chop and i fall. I know its a matter of technique and that I shall not extend my front leg that much but wont the extra rocker help with that? All this rocker- wind relation has been troubling me for quite a while, and although I would prefer a board with some good rocker to have the most comfortable ride and landings I do not want to be handicapped below 16-17 knots. maybe I shall loose some weight.

Also I have noticed that many people are against carbon boards for some reasons, and truth is I wanted to avoid them and move to a wooden board altogether. I will try and get a demo of the asylum and see how the 5cm of rocker feels. I also think asylum is not exactly for my level just yet as you guys have said but since I progress quite well I am willing to buy a board where I will grow with it. maybe I will wait for the vision model as well which has not been announced yet.

The only thing that troubles me with the 4cm rocker board the mk5 is that even in the video which blankforce has produced the guy riding it, rides in flat waters. you will tell me its just a commercial where they will try to produce the best results for promoting the model, but even from youtube users that ride mk5 most of them use it in flat waters so I am thoughtful about its capability in what I consider heavy chop.

thank you
george