I agree. The blacks of the P800 are notably improved over the previous-generation inksets. I'm especially impressed with matte papers, where blacks have historically been a weak point.
My initial conclusion with the P800 was that the image quality improvements were subtle enough that if one had a properly operating 3880, there wasn't much in an upgrade.
Now, after six weeks of heavy use, I've changed that view. For those who want a bump in print quality, the P800 warrants an upgrade