The F4 uses a TTL full-aperture metering system. Three modes: • 3D Matrix Metering - Range: EV 0-21 • Center-Weighted Metering (60% sensitivity concentrated on the 12mm diameter circle - Range: EV 0-21 • Spot Metering - Range: EV 2-21 The area metered is represented by the approx. 5mm-diameter circle in the center of the viewfinder
The F100 also uses a TTL full-aperture exposure metering system With three metering modes: • 3D Matrix Metering - Range: EV 0-21 • Center-Weighted Metering: Approx. 75% of the meter’s sensitivity concentrated on the 12mm diameter circle - Range: EV 0-21 • Spot Metering: 4mm diameter circle (approx. 1% of entire frame) - Range: EV 3-21
Like you, I never found any difference in performance, even when shooting finicky slide film with no latitude, requiring precise metering in either of the three modes.
Handheld meters with spot metering are usually a 1° meters. Are the spot meters on the F4 and F100 up to the task for usage of the Zone System? I would say yes. But I would wait for experienced answers. I've never used the Zone System. Maybe I was not very interested in it then to dedicate to learn it. Because of that it took me a few years to understand it