I'm very interested in this too. We're looking at triple glazed aluclad, most recently visited the Vindr and Nordan showrooms. Wasn't as impressed with Vindr as I expected to be. Nordan seem to be a top of the range product, but that could have been down to a better salesman.
Nordan are quoting 0.82 average u-value for their 3G, 1.2 for their 2G.
Vindr are about 0.9 for their 3G and I think 1.4 or 1.5 for their 2G. It was very hard to get a straight answer from the guy!
Looking forward to hearing some feedback on suppliers. Thanks