Here is a link to a completely unbiased review of the Valhalla: http://www.wakeboarder.com/display.phtml?a=867
Maybe you could demo one and give us your own review? I think you might like it. Just watch out for the knives.
I have ridden all of the boards you mentioned above, and the Valhalla definitely evolved from the Demented. To me the Valhalla seems a little faster then the Demented, popped just as well and landed softer. I think the added speed comes from the Crook fins. They really allow you to get the board on edge and hold it all the way to the wake. If you liked the ride of the Demented you will love the Valhalla!