My vision of railgun drones (because missiles with weapons may as well be called drones) involves them accelerating all the way to the target.
(depending on how the damages work out, they might not have to do this. Burn 50% of delta-v then reserve for course correction might be more than enough)
Drones can pack much higher fuel to mass ratio since they are one-shot (and can burn all their delta-v) which means the closing speed of the drone will be obscene, the drone can then fire its railgun shells at all targets and then attempt to ram something.
If the drone itself hits, that thing is gone. Armour, fancy shields, uber big moon-sized battlestation, all gone. Nothing will survive a 5ton object hitting it at 60kkm/s. Maybe not even planets (the planet itself will live, not sure about anything on it)
And at 60kkm/s relative speed, any hit from railguns will also likely blow away vast amounts of opposition.
...
You know, when this all comes out, I'm totally going to make fighters. No carriers, just really really small ships. Single weapon or missile launcher, that's it. Jumpships and support (like radar and coillers) will probably be bigger, but I don't intend to put those on the line of battle.
When every shot is lethal, you want your enemy's shots to overkill as much as possible. Why build big battleships when they die to one shot anyway? Better to have many tiny ships and eat the inefficiencies. They'll pay you back when the lucky 30% of your stuff comes back, instead of 1 lonely ship that lived through a mid-range nuke.