I worked with an Indy for some time and what was really cool - besides the smooth and fast reaction to user input you mentioned - was that the UI elements were scalable. If I remember correctly they were vector and not bitmaps. Back then I thought that this will soon be the norm. I'd never imagined that we would still be struggling with this more than 20 years later.

EDIT: After googling SGI workstation models I think what I used was actually most likely an O2[1]. Great design, I remembered its distinct look even after so many years.

[1] https://en.wikipedia.org/wiki/SGI_O2