I doubt there's much torsional flex at the rear-wheel at all unless you have radial spokes. In which case, the hub will wind up the spokes until it increases the spoke-tension enough to balance the torque. With any amount of crossed-lacing at all, you'll be stressing a spoke in tension and there's no amount of torque a human can apply that will stretch a single-spoke, much less 28-36 of them. So torsional-rigidity is pretty much equal for the types of power delivered by a human.

However, lateral rigidity is a wheel's weakest point. That's what you're feeling in a sprint due to the lean-angle. This applies a lateral load proportional to the sine-function of the lean-angle. The more you lean the more the wheel flexes. What determines the lateral rigidity is then the triangle formed by the two spokes and width of the hub-flanges. The bigger the angle of the spokes coming into the rim, the more laterally rigid it will be. That's why track-hubs use large-flange hubs, to make the base of the triangle wider. The most laterally-stiff wheel you can build would then be with large-flange hubs and radial lacing.

Some people say that the wheel is also stiffer vertically with radial-lacing, but I haven't been able to feel it or to quantify it in that direction. It's tough to figure because the tyres will flex and compress due to your weight about 100x more than the wheel itself.