I havent used any valandre bags either.
there are reveiws by Doug Jhonson and carol crooker on this site for the Shocking blue, and mirage bags.
I also have been looking into a valandre bag for sub 0 snowshoeing and backpacking, and I have read only good things about the company, and their products.
all their bags are made with a differential cut, so you get the most out of the insulation.
for maximum warmth I think the cut is appropriate, I dont have any first hand experience, but I ave read a few reveiws, and I cant recall any complaints
If you are looking for maximum freedom of movement, but still want a bag that can retain warmth adequately, check out montbells super stretch bbag, if you havent seen them already. I have two, and love them. but im looking at Valendre for a extreme cold expedition bag.