I think they need at least a lvl 1 head to deal any damage. And if you're unlucky you'll soon run into armoured missiles.
Something I want to test is packing a fighter full of engines and a few microwaves, and then rush them towards their target, like manned missiles. If even only a few survive, they had better hope their systems are EMP-protected, or they'll be flying blind through a hail of missiles. Of course they'd best be launched from a mothership with powerfull anti-missile protection that carries them up to the other ships max beam weapon range.
Also, the 4-shot modifier on railguns seems like it'd make some very good anti-missile systems. Anyone tested them yet?
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Forgot to say, I can't colonize mars this time
Gravity..
Take a look at Titan, a moon of Saturn. It's cost will probably be around 5-7, so pack plenty of infrastructure. It's a lot colder then Mars, but has a higher gravity and with an atmosphere of 1.74 atm (95% nitrogen, 5% methane), it could be easier to terraform. You just need to strip the methane, add oxygen and then fill up with greenhouse gass (In no particular order). No need to pump a metric carpton of nitrogen into the atmosphere. If you want to be fast, you could even forgo stripping the methane, which will limit it's cost to 2 because of a toxic gas. I can't say for sure if upping the greeenhouse factor to 3 actualy makes the temperature high enough to be of use though.