I used version 4 before upgrading to version 7. Both have an emense capacity for data. When I upgraded I had over 25,000 individuals and 1,500 source citations. Most of my entries have notes and many have extensive notes.
As for Family TreeMaker, at 18,000 individuals it siezed up every time I tried to use the relationship calculator. Tech support couldn't find a fix and instead gave me a free upgrade--which did the same thing. That's when I moved to Generations.