I've used a P25 for about two years now, both on a Linhof and on a range of Hasselblad V cameras. I've been delighted with the P25 except for a couple of small issues that the P25+ seemed to address. However, the upgrade price for the P45+ wasn't much more than for the P25+, so I ordered the 39MP back.
For large fine art and display enlargements the extra pixels may come in handy, but for 99% of the commercial work that I do 22MP is plenty big enough. Once you get to full bleed on a double page spread at 300dpi it's pretty much the end of history!
So why did I trade up? It seemed to me that although 22Mp is enough for my purposes cheaper cards and faster processors means there's not much downside, and 39MP will protect the future value of my investment. Although I also suspect that the absolute image quality I was getting from two stitched P25 shots (using the sliding carriage on the Linhof) would be better than a single capture using the P45+ with an appropriately adjusted lens. I hasten to add that's just a theory, and as I won't have the P25 and the P45+ together to experiment with it'll probably remain just a theory!