I have an N80. I bought the SB50DX. I shot 3 rolls of film and also played with its' built in slave feature. I shot with my Tamron 28-200XR and also one roll at night with a 50mm 1.8f (which is a pretty fast lens). I was not happy with the results. I am sure that is due partly to my own inability to get the most of out my equipment (being somewhat of a beginner), but people were not properly iluminated that were 15 feet away. I returned the SB50 and bought the SB28 (and the SU4) after just a few rolls with the SB28 I can clearly see the difference in the power of the flash, not only in the subject (people) but in the eveness of overall lighting too.
I did not have great luck using the SB28 as a slave with the SU4 so far- if you want to read more about that, it was in a previous thread (which I never got a good reason for why the TTL did not work properly)
Also I am a firm beliver that its more knowing how to use it than what you are using. I have lots to learn .. .. ..