For example, I have an Apple PPC Upgrade card 66 Mhz, and it works great. This allows you to run Mac OS 8.5 - Mac OS 8.6 on Quadra 950, but I didn't like how it works, too slow memory for these systems. But as an experiment - why not?
If you manage to find DayStar at 100 Mhz, it will be 100 Mhz.
Recently at an auction in Japan, I saw an 80 Mhz with memory banks, I also participated in it, but the final price was higher than I could have paid that day.