I've been using my P645 for about three years now. It's an awesome camera.
Mine was used and in very rough shape. It's never had a hitch and i'm glad that I bought it. Sometimes I do wish I could change the finder or swap backs in mid-roll but I can live without this.
The 75mm lens is definitely outstanding.. There isn't a bad lens in the whole lineup. The camera is quick.. It's a big spotmatic with an led viewfinder. The AA batteries last for atleast 150+ rolls and I change them once a year out fear.
Also, used lenses sell for a reasonable amount. Are you sure you want/need to sell or trade your fuji? Having both the fuji and pentax would definitely round out your outfit... Just my thoughts. The pentax is great IMHO.