P class on AC is one of several sweet spots (40% of the distance as PQP), as are deep discount Premium Economy fares on a number of carriers while the absurd PE sales last (sub $1,000 for long distances). The biggest plus is that the most efficient way to run for status now tends to be in the premium cabins, whereas previously mileage runs were much more cost effective in Economy.

The discussion in this thread has more details: Earning Status (PQP) on non-016 Tickets and Partner Metal