Interesting threads, thanks to all contributors.
Couple of opinions:
1) 1% is fine per rudder if there is not too much windage. Use them both at low speeds, the front one at high speeds.
2) Big rudders with high bearings do need strong shafts. However, they can also be much thicker and carbon is pretty strong stuff. To the best of my knowledge, no one has broken the spar of a dagger type rudder or the shaft of a spade type yet.
3) Smooth foils make a big difference, as do aligned ones.
4) The only difference that affects the boat balance that I can see between keels/daggerboards etc under the lee hull and oversize rudders mounted on the inside of the lee hull is the location of the drag. I am pretty sure that we could have sailed Rare Bird with a bucket dragged from the middle of the beam without it affecting the steering. Therefore, until we get some proof positive that keels etc work, I remain of the opinion that oversize rudders not only work, but that they are far less hassle than any other combination. That is not to say I am against experimenting with them, I encourage everyone to do that. Also, if you are putting keels on with the intention of drying out on them, they need to be very strong as the odds of bouncing up and down on them on a beach are high. I prefer to use a couple of car tyres under the hull to dry out on. They allow you to reach all of the underwater area (admittedly in two tides), and can double as fenders, line springs and a drogue.
rob