Originally Posted by
StouterTaru
If you have 940 TP or less every 3 seconds for the entire fight, you will get the same amount of TP regeneration for the same amount of time, period.
If you get to the point where you can use Invigorate without wasting any TP 10 seconds faster, then that's 10 seconds each successive Invigorate happens, and 10 seconds you're more likely to get an extra one in, or burn up the TP from it before the end of the fight.
Also, skill speed affects speed of autoattacks, which are 25-30% of your damage.