I've just spent a happy hour or so testing the motherboard chipset slowdown utility called "Throttle". I tested it out on the following rig -
Pentium III CPU (500mhz)
Supermicro board (P2 or P3 CPU, slot 1, 440BX chipset)
100 FSB (can be set to 66 if required)
Running the utility gave me 7 speed options to choose from, ranging from 12.5% throttling of the system, all the way up to 87.5% throttling of the system.
Test 1) I ran Ultima 6 without using "Throttle" at all. In summary, the game ran way too fast.
Test 2) I ran throttle and selected 50% slowdown. Running Ultima 6, I could see a notable slowdown in speed, but the game still ran too fast.
Test 3) Set Throttle to 75% slowdown. The game seemed a fraction too fast, but I felt like I was definitely "getting there"!
Test 4) Set Throttle to 87.5% slowdown, which for my system was the maximum amount of slowdown that Throttle could offer. The game now seemed a bit too slow!
So, for my Intel 440BX chipset-based motherboard, 75% throttling seemed to be the best choice. It wasn't perfect, but so much better than not using Throttle at all.
According to the Throttle readme file, alternative chipset-based motherboards to the Intel 440BX (such as VIA) allow the Throttle user to select about twice the number of slowdown increments, which would allow the user to more finely-tune the throttling amount.