The engine will hit the objects limit well before you really have to worry about performance.
ed: well, depending
Well that negates the whole point, right? If you won't be able to have 50k maxim "sprites", then it's true that you *can't* have a thousand-drones swarm firing maxim. I mean what's the point of having that and them not being able to do what they were built for.
OTOH, one could have instead a smaller swarm of drones, like
fifty, they would appear to be "lots-f-them" to the player, and with maxim cannons, they would be *very* powerful indeed. If each drone has one canon, they would have a firepower of 170 damage points per second, and with 50 of those we are talking about 8500 per second, continuous, for the whole swarm. That's a Deimos in less than 10 seconds.
Now granted, there would be a degradation of the prowess there, since we would see the Deimos, for instance, blasting off the drones with their AAA beams, and flak, etc.
But this can be, of course, fine tuned. And when drones come back to the swarm frigate, they could be "replenished" for a second attack.