The approach to speed has always been misunderstood.
What is important is time to fill the 100% TM, not the speed itself.
The usual approach is to say that turn meter fills twice as fast for a character with a Speed rating double than the other. And it should be worded as the time needed to fill the TM is half.
Thus, TM fill is inverse to Speed: 1/Speed
To make it simple, we can say that the seconds needed to fill 1%TM = 1/Speed
Character A with 200 speed would take 1/200 to fill 1%TM
Character B with 100 Speed would take 1/100 to fill 1%TM.
To get the full 100%TM would then be 100/200=0.5 seconds for character A and 100/100=1 second for character B
If you get a bonus TM of 40%, the time needed to fill the TM has changed, and you only need to fill the other 60% to get a 100%TM
For character A would be: 60/200 seconds = 0.3 seconds
For character B would be 60/100 seconds = 0.6 seconds
Now you can convert the seconds to 1/x to get the speed that a character would need to fill this 100% TM in the same time that the character with the bonus TM has reached it.
For character A: 100/0.3 = 333.33
For character B: 100/0.6 = 166.66
Use the actual speed of the character and the actual bonus TM gain to get your data
