I do ALL my work on good old KR64. (KM25 isn't available here, and hasn't been for quite some time... since '98.)
Keep in mind, every camera is different... two F5's are slightly different. I found the sweet-spot on my F90x is doing -2/3 stop. Sounds like a lot, but on my camera, that setting gives me perfectly exposed shots, time after time, roll after roll, even with my converter at 280mm. But I'm using the "fast-glass", so it would be expected to obtain excellent results, but getting under-exposed slides with 50mm??? Hmmm... if you have it on spot-metering mode, and you're always shooting at glare, you'll get underexposed slides because your camera will over-compensate by giving you a higher shutter-speed than needed.
What other people think of you is none of your business!