Which Apple displays were you using that ran at 30Hz? Apple I, II, III, Macintosh series, all ran at 60Hz standard.

Even interlaced displays were still running at 60Hz, just with a half-line offset to fill in the gaps with image.

I think you are right, I had the LC III and Performa 630 specifically in mind. For some reason I remember they were 30Hz but everthing I find googling it suggest they were 66Hz (both video card and screen refresh).

That being said they were horrible on the eyes, and I think I only got comfortable when 100Hz+ CRT screens started being common. It is just that the threshold for comfort is higher than I remember it, which explains why I didn't feel any better in front of a CRT TV.