I've just bought a 2/3 oneill physco RG8. This suit unlike the physco 3 is all 2mm apart from the chest/back panel. Unbelievable flexibility, and being a chest zip seals very well. I tried the earlier chest zip Oneills and they didn't impress me much, but the lastest version I can not fault. I have a largish neck and still find it very comfortable. As long as you use the left arm first theory, they are nearly easier to put on than the rear zip, as everything pops into place as the suit comes up.
It is almost too warm for perth winters so the physco 3 would handle any Aussie conditions.
There is another thread on here with the Dutch guys saying the 5/3 is too warm unless its below 5 or 7 deg

. I believe they mostly use 4/3.
My Physco II lasted 3 seasons of surfing heaps and windsurfing more, without ever washing it out (or drying it for that matter