[Suicide Junkie]

I suppose it depends on your video card, but the pirates in my P&Nism mod use 200ms, 6 damage meson blasters as anti-ship weapons.

Looks somewhat like a starwars battle, and dosen't even dent the framerate. Each bolt is only 2 polys.

I also don't see how a tiered system will help very much.
All the weapons will still be firing on the nearest incoming seeker. You only get an advantage if the Tier X weapons kill the first missile before it reaches Tier X-1, AND if the Tier X PD has a very long reload time, such that the second missile reaches X-1 range long before Tier X can fire again.

You still need to make the shots move very fast, which solves much of the problem with stock PD already.