Just realized I was stacking my astro shots wrong for two years

I have been into astro photos for about three years now and I always wondered why my final pics looked so grainy compared to what other people post. Last month I was messing around with my DSLR in the backyard here in Boise and I finally figured out my mistake. I was shooting at ISO 6400 to keep the stars bright, but I never took enough frames to stack, maybe 8 or 10 shots at most. Then I read that most people stack 50 to 100 frames at lower ISO like 1600, and when I tried it on Orion, the noise just disappeared. Two years of bright but noisy Milky Way shots because I was too impatient to let the camera run longer. Now I want to know, how many frames do you all usually stack before the result looks clean enough for you?