For film I shot the F90x and the F4 but I loved the F90x more because it was smaller and lighter. The F4 was an amazing camera. Like others have said very rugged and sealed with great focus and a great overall feel. I'm not sure about the F5. Why not shop around especially on ebay for the F6??
I'm interested in getting a used F90x, or F65. Now I know the F90X has better features, but the F65 supports VR and appears to have better a better grip. The F90X only supports AF-S, but it also has a tougher body, and a slightly bigger viewfinder at 92% vs 89%, not a huge difference of course. I can get either cameras for around $47 US, which would you choose?