Engine power tech is cheap compared to your base engine tech, and missiles profit greatly from it. I suggest researching it before making a missile-centric fleet.
If you don't, cutting down severely on missile range doesn't get you much, and 5m is too close for comfort.
One of the things that can make missile fighters work is that they can deliver their ordnance before they are detected, this favours the smallest practical fighters with moderate-range missiles.
Warhead 5 is also not a very happy number. Square numbers get you an additional layer of armour breached, n^2+n (6, 12, 20, ...) gives you 2 damage on the deepest layer. So 4 is good, 6 is good, 5 is nothing special.