Tm gain after turns start makes it very difficult to calculate an effective speed because you are no longer comparing a 100% fill to a say 80% fill
What you have to look at is tm jumping if that is happening based on speed and current tm fill.
First turn
If characters A and B has 200 speed and character C has 190 speed
Charater C will be at 95% TM when Charater A and B hit 100% TM If character A goes first and does something that gives character C 5% TM then Charater B and C will be at 100% TM and RNG can make Charater C go before Charater B even if character B has higher speed.
TM manipulation does really boost speed just makes it appear as such because it makes it so speed has to fill less of the TM bar
In the above scenario the effective speed of character C is 100/95 = 1.05
But if charater C had 195 speed instead of 190 his effective speed drops to 100/97.5 = 1.02
So as you can see a 5% TM doesn't always add the same amount of effective speed. Effective speed can only really be looked at when starting with 0% tm and looking at starting TM boosts like Zaul or bb8, if the TM boosts comes after the TM bar fills effective speed can go all over the place.