500 or 1000 seems about right. That being said, there are a lot of variables. Could the Krayts combine powers to form some type of mega Force attack?
IIRC The Jedi Path stated several Jedi can join powers to form a Force Storm(the type Palpatine used), and some of Palpatine's flunkies had the same ability. What if 500 Krayts held their ground with lightsabers while the other 500 used some type of hyper Force lightning storm or Drain attack/Dark Transfer?
Remember, Krayt's Drain was strong enough to severely injure Abeloth. And remember that when a bunch of random Sith mooks used the Thought Bomb on Ruusan it was enough to wipe out a nice chunk of the Jedi Order.
Considering the type of damage the likes of Exar Kun, Nihilus, Vitiate or Palpatine were able to do by themselves, the possibility of a combined attack by 500 Force users of the same caliber would be theoretically off the charts.
Would the combined might of 10k Jedi be enough to defend against such an attack if they used some type of Wall of Light power?
Then there's Reborn Krayt's skill with the Shatterpoint ability. IIRC only Mace had it on the Jedi side. Assuming some type of massive, open field, medieval type of battle, how significant would the Shatterpoint ability be in terms of exploiting tactical errors? Would it allow the Krayts to rout the Jedi the way Alexander routed the Persians at Gaugamela?