Loumardes
Okay, finally did enough tests to give you proper feedback.
First off, you should remove the tractor beam, as it pushes you over the 750k price cap and sends you into the 800k range instead (or about 775k if you cut some other stuff). I had my modification of the diagonal 'Spearhead' (made by Astrum, 747.400 credits; it's quite old but wheights about half as much as your Rail and has ~100 crew) do a AI battle with your design and it even won using only one half after I targetted the tractor beam at the outer edge of one wing at the start of a battle. I'll have to test that, but I'm pretty sure the beam won't do much in mp, as even the AI could stay pretty close to its desired position.
Second thing I noticed was the enormous weakness the center railguns pose. Even the AI ended one battle almost instantly be destroying one of those, as they chain explode even the reactor, taking out the control room and all other railguns in the process.
The design is also extremely weak to ramming, as all firepower is focused on the from and the design isn't really fast enough to get rid of anything on the sides.
Generally, the current design explodes way too easily and can't keep up with most other ships regarding both speed and damage potential. As with all rail-based ships, it's rather difficult to hit any critical enemy systems, while the own weakpoint has to face the enemy whenever shooting. You should first make sure to fix the reactor explosion when the center railguns go down and then try to reduce wheight and cost (unneeded armor/doors) to give it more speed.
And have the Spearhead for testing:
Diagonal ships generally deal more damage than walls thanks to having more weapons facing the enemy at once, but I didn't find a proper wall in that price-range and am somewhat short on time...
(Ignore the odd-looking reactors and quarters, I saved this when having Kroom's Forge activated, but it will load into your game just fine.) That ship brings back memories...