I've only been sailing for 2 years, so my experiences are very limited, but, in less than perfect conditions i think i would stick to my CA SL55. The SL55 is no slouch though, i've had it over 41 knot 2sec and 36 knot 5x10. Just a great board in the rough with it's slalom rocker.
I've had one session on a CA 40 and trying to stay upwind, through chop was quite difficult. I ended up walking more than sailing

, but found it much quicker to get to speed, off the wind, which i think helped my 10sec. Same 41 knot 2sec as SL55, but 39.8 knot 5x10

.