just for grins, I'll muddy the water a bit.

why limit your double blade paddling to a solo boat ? - if the double is so much better, why not use two in a tandem ?  I've seen that once, with an aluminum rental on Quetico Lake.  Yet, many of the same people who recommend a double blade (not necessarily on this site) have never recommended the use of double blades in a tandem canoe that I have ever seen.