I think you are correct about the weight. Peter Cranes boat Eirena is very light and sails very swiftly. I have been experimenting with sailing to windward in light airs with one keel fully raised (it was stuck up for a couple of days) and she was certainly swifter to windward like that. I also know that I gain almost a knot motoring in a calm when I fully raise both keels.
Not sure I would want to reduce the weight of the keels though – they have a low ballast ratio as it is. Of course it could be carbon fible keels with lead in the bottom! that would increase the righting moment without changing anything else.
I suppose my final comment would be that they are already fairly fast OFFSHORE. As in when there is wind F4 and above they keep up with boats which are significantly bigger. Perer Crane and I sailed from Falmouth to Penzance in winds of F4 to F6 from the SW. When on the moorings outside Penzance harbour we recieved comments from the crews of the 35 ft boats which also made that passage on the same tide along the lines of “those boats are fast, we couldnt catch you!”
To me it is important to have a boat which feels secure at sea, so while it might not be as fast as boats intended for racing, it inspires confidence in me. I have taken it out of shelter in some pretty strong winds! So I dont actually feel that the performance needs improving!