According to bit-tech (http://www.bit-tech.net/hardware/gra...-for-folding/5), the GTS 450 still has that crown. Second is the GTX 460 768MB!
[Look here] Scroll to the graph at the bottom.
The PPD isn't averaged over enough WUs, and overclocking isn't considered for most cards - for example my OC'ed GTS 450 gets roughly 9k ppd average (generally 8.9-9.2k), and spikes up to 15k on some WUs.
The power efficiency numbers are completely meaningless, because they considered the power draw of the entire beefy folding rig on an oversized PSU, rather than just the power from the cards. Which means the highest PPD producing cards will always look the most efficient, and the numbers are meaningless when you're looking to choose an extra card to run in an existing system that is on anyway. At very least they should have tested the power draw of the system without a gpu and subtracted this from the folding power for each card, which would tell you the PPD/W for the card rather than the system.