You may have the math to back it up (I know I don't!), but it seems to me that twelve pounds of additional weight at the extreme bottom tip of the keel would have more of an impact on righting moment than 4 pounds on the rail. Both the hiking position and the bottom of the keel are about the same distance from the axis of rotation (about 5'+ or -). Seems to me if you go to the trouble of adding the depth, mixing in a generous quantity of lead shot would be well worth it.
The thinner leading edge and the longer chord length make a significant performance difference upwind. I find I point better, accelerate a bit faster, and have a more stable groove in lighter air.
