check this link:
Dead Link Removed
it seems F6 is fine:
"Infra-red film can be used in most Nikon 35mm SLR cameras, the exceptions to this are the F80, F75, F65 and F55 all of which use a frame counter which uses infra-red light and should not be used with infra-red film as fogging may occur.
Please note that precautions should be taken if using infrared film with a camera that has a "Film confirmation window". Infrared light can pass though the foam light trap and fog the film (the light trap will block light that normal films are sensitive to, preventing fogging). To prevent this, cover the "film confirmation window" with opaque "gaffer", "duct" or electrical insulating tape to prevent infra red light leaking through and causing fogging on the film"