Phill, by the resounding silence I guess there's not much experience around about distance racing cats with wings (why does this sound a bit similar to "pigs will fly" ). "Cat's with wings, flying mandatory".. Ok, I'll put a leash on my sense of humour from now on!
Was there any cats with wings or racks in the 'experimental' Worrel races?

Simon, as far as I can understand racks aren't that bad an idea. Yes, the racks will add a bit more weight compared to 4 more feet of beam extrusions (or carbon, what do I know what people will build). What's important tough is the righting moment (RM).
A 10 foot wide cat will have an advantage in RM as hull weight comes 1 foot further out. A typical hull will perhaps weight around 35-40Kg's (??), so this is not a large advantage. Another point is that the axis for heel is a bit further out on a 10 foot wide boat compared to an 8 foot wide one. But by adding a 2foot rack on each side, you are able to move your bodyweight out just as far as the 10 foot wide boat and this is what's most important. In addition, the boat with rack's have the mast further to leeward, which gives a better weightarm for your creweight. (I haven't done the math, so I might be totally off and wrong). In addition, the 8 foot wide boat can get up on one hull earlier, which gives about 20% less drag and better windward abilities with the "new" hullshapes..

(Ok, now I have really done it. Talked myself into actually liking the tought of a 8 wide boat with racks)

I think your envelope is a bit to wide and expensive, we will probably not have much success in building such a class (it becomes to expensive and time intensive for most). Loosing the jib is probably not a good move for a distance racer, but might be smart in a pure upwind/downwind machine.
I had the same opinion as you earlier on, but after spending some time on it and receiving comments from others I have reconsidered. Now I think it's sensible to stay within the B-class envelope, limit mast height to 9.5 meters, weight to min. 140 kg's and 50 square meters of sailarea max. There is still plenty of room for experimentation if someone wants to tinker with their boat.

Dave, I think the current 20 footers are to heavy. I recieved some opinions in a PM, and one of the major philosophies lined out there was that minimum weight for a class should be based on a set of plywood hulls. I think thats a very good idea, as plywood hulls are something everybody with the inclination can build at home during winter. And if it can be buildt in plywood, manufacturers can achieve the same properties with composites. The stellar example is the Taipan4.9 class where timber boats are just as competitive as glass/epoxy boats.