The 4 cross pattern (on a wheel with 36 or more spokes) will transmit torque more efficiently than 3 cross since the angle that the spokes make with the hub will be closer to tangential. The vector resulting from a three cross lacing pattern will not be quite as efficient, but it will be close enough on a 36 that I doubt if you will be able to tell the difference in wheel longevity, assuming you tension the spokes properly and, as Mark said, properly stress relieve the spokes and seat the heads on the hub. With either pattern, all the power will be transmitted from the hub to the rim. The difference is that with the 3 cross pattern, the hub will deflect rotationally (wind up) a miniscule amount before the full torque is transmitted. This amount is not likely to be detectable to any but the most sensitive instruments and I doubt that it would impact the lifespan of the hub. The 3 cross would be a tad lighter, of course.
On thing that I can only theorize about is the fact that as you approach true tangential spoking, that two adjacent spokes on the hub approach 180 degrees of angle with respect to each other. With the small amount of aluminum between adjacent holes, it seems like the localized stresses would be larger than if the spokes were angled out at a smaller angle. That situation would place reactionary stress in a direction where there is more non-perforated material to allow the localized stress concentrations to be lessened. I'm not sure if this will eventually manifest itself as a difference in fatigue failure between two identical hubs. The fact that hub failures are not a common mode of wheel failure (except in radial lacing situations) leads me to believe that the differences are too small to be of concern.
Of course you know that this does not apply to front wheels since the spokes transmit no torque. However, many hub manufacturers state that tangential lacing voids their warranties since the stress patterns from radial lacing can lead to premature fatigue failures of the hub. In my opinion, a two cross pattern is a good compromise for minimal weight penalty without sacrificing longevity when using these hubs. Some hubs are designed for radial lacing and of course, for them, this caveat doesn't apply.