Thanks everyone for the insights. It is very helpful on this site that people comment on how a board responds to different snow types as it aids an informed decision. With that in mind, I think I am going to go for the 156cm Goat. My major concern was that it could get me round the resort on the hardpack and be stable on long run outs at the end of a tiring day. I think looking at the board, hearing peoples experiences and even the fact that Gnu have made a split reassures me that this board can be the good off piste machine that is my priority but I have also had the all rounder aspect confirmed.
Basically, the Impossible is expensive and it is not clear what it is really for, just a souped up Riders Choice. The TRS/ Riders choice look decent but sacrifice something in trying to do it all (as with the Custom, BSOD etc.) The Trice is too wide for my size 9s. The Billy goat is fast, agile and floats wel- I love the trees and this board grabs me better than the Pjeonix seriess and seems more suited than the Banana magic or Dark. not too familiar with neversummer but I would imagine they are just as good.
As tempting as trying to butter with the young guys is, it is obvious that no do it all board exists and I would hate to sacrifice what I really need; not that I could compete with the kids anyway. Also, I don't think I would waste a good powder line, that I hiked an hour for, on riding it switch anyway (although I am hearing what Snowolf says that you don't need a true twin, especially in the resort.)
I called the local Gnu dealer in Zurich and he has every board but the Goat. He also said it could be difficult to order as it has limited production. Sadly, I may not be able to get back to Canada at Christmas this year so hopefully I can find some way to make this purchase. If I am succesful I will put up a few coments about how it rides (or rides me). But somethings got to give as my current set up is well past it's best days.
Again, cheers for the info. Snowolfs epic review of the 2012 was particularly interesting- especially as he had one hardpacked day and one powder day to talk about.