I'd imagine the difference is minimal.
The G3 pattern basically is 3 spokes all at equal tension, originating at a single point. The G3 geometry will give a better balance of spoke tension, but you rely on the rim stiffness for the gaps between the spokes. Since the rims are semi-deep section, the rim is inherently fairly stiff. Basically, you have a rim suspended by a set of triangles. It will be very stiff at the triangle and more flexible away from them. Its also much easier to reinforce the rim at the spoke point.
The 2:1 pattern probably results in a bit more variability in the tension, but you'll have a more uniform stiffness across the wheel. This design is likely better as the rim gets lighter and shallower, but for a fairly stiff Al or CF wheel I could see the G3 design being better.