I just got back from Midway Plywood in Lynnwood, WA.  www.midwayplywood.com/‎

They have supplied many of my plywood/epoxy projects including the two Lake Victoria ferries. I had gotten a report that the 3mm plywood (2.7mm actually) was such poor quality that it was not usable. I just bought some very good sheets, so this shipment is better. It is Seal Brand which I have used before. The price has gone up about 50% in the last 6 months to $17.95 per sheet before tax.  It is about half the price of 4mm BS-6566 plywood at Edensaw Woods. http://www.edensaw.com/

I have not D790 tested it yet.  Possibly Thain Boat has.  I’m guessing the numbers would not be as good as BS1088 but close.