Others have brought up the issue that 500 total reserves is too limiting and final. Especially for pure psionics where running out equates to a death sentence. It feels so final and sudden, especially on certain psi-focused builds.
Suggestion - Why not change the penalty to behave more like gun durability? You could do something like, As the reserves go below < 20%, chance to hit with psi spells start to lower, all the way to 0 psi reserves where the chance to hit is 50%. This would bring the system a little closer inline with the durability system used by guns, and also not be so final, in the sense that fights can still continue even when reserves hit 0 (just not very efficiently, like using a broken gun). I can see how some may not like this, as the last 100 psi reserves introduces a new 'chance to hit' penalty for psi spells, but I think its a good compromise that would allow long fights to not necessarily end so abruptly. I'd like to think of Psi Reserves as reflecting mental fatigue, not an empty gas tank.
Another thing I'd suggest while we're on the subject. Psi Reserves feels like something that should increase with level, and/or willpower. It seems a bit strange that a level one greenie would have the same amount of mental/cognitive reserves as a level 30 vet. Or that a mental wizard with heroic willpower wouldn't have a greater amount of psi reserves than a lovable brain-dead oaf who can punch guud.
All in all though, I appreciate the refinements in the last two hotfixes. Keep it up.