May I make a suggestion for the CTB turn display?
I've noticed there's an issue with people not understanding how your CTB works compared to your ATB when they practically function the same way (both are tick based)... I had this issue myself but personally I think its more to do with visual clarity than the mechanics themselves.
In your ATB you can clearly see how speed/gauge-consumption is affecting the turn order, you can clearly see each gauge in comparison with each other, especially with your enemy gauge addon. This makes turn order and the effect of different 'speeds' clear both for the 'maker' and the 'player'.
The problem with your CTB is, it only shows the order and not how much 'time' is in-between each battler. This means as you've already explained earlier, even with a speed of -2000 you will still immediately act if the next battler actually has a more than 2000 ticks till their turn. While this is fine in function there's 0 visual cue, meaning that it's hard to understand what's happening.
With this in mind I would like to suggest having 'empty slots' which represent a large gap between battlers.
For example, for every 500 ticks between actions/battlers there could be a blank block. So visually that skill with -2000 speed will practically act immediately if there are 4 or more of these blocks between the user (2000+ ticks) and the next person to act, but will act later if there is only 2 blocks (1000-1499).
I don't know how difficult this would be to implement, but personally I believe it will make the effect of speed a lot clearer for both the 'maker' and 'player'.
To better explain what I mean, here's a screenshot from
Mana Khemia, notice the 'gauge' at top with its 'blank spaces'. This way you can tell there's a much larger amount of 'time' between the red head and the blonde compared to the bear which is right behind blondy and closely followed by white head (after he finishes his action).