Plus-X is good at 64. I've used it at 64, box speed (100 or 125 depending on if you're using Kodak's or Freestyle's box), and 500. I've read you can push further, but I don't need to.
I personally rate Plus-X at 500 and develop for 11 minutes at working strength (no dilution). It's perfect for the type of work I do at that point. No contrast filters are necessary if you have a good negative. However, that's probably true for most films.