I am running a 3-bladed Autostream on our T37http://www.westbynorth.com/AutostreamShaftDrive.aspx
I cant recall off the top of my head what size it is but if you contact them West by North Enterprises - Contact Us
they will assist you in finding the proper size and will preset the gearing for you.
I cant say how it compares to running the original two bladed prop since we purchased the boat with the Autostream, but I can easily do better than 7 knots SOG at about 2800 rpm, and 6.5 at 2200. I also cant comment on the fuel consumption as my W50 is not running well
I would add, many I know have had wonderful results with their Campbell Sailor fixed prop. West by North Enterprises - Campbell Sailer
Member Mainesail has some very good data about it on his website and here I believe.