There are a few other tips when you choose two of the same weapon, such as in a Herc2 loading up 2 PromS or PromR and making them fire about 40% faster. Here's the lowdown on it...
Your keyboard is probably set so that the . key cycles through primaries. Set on the second gun bank and when you're close, start firing. About half-way between each shot, hit the . key and it switches it to fire the first bank between shots of the second bank. Damage stays the same though you fire much faster. You have to reset this each and every time you stop firing, or it fires both banks at the same time, taking away the advantage of speed.
The Ursa (highly recommended) and the Medusa (mostly hated) both have top-mounted automatic turrets. The Ursa turret is based on the UD-8 Kayser (think of a cross between Subach HL-7, Prometheus S, and a wicked-cool silver shot) while the Medusa's turret is based on the Prometheus R. In short, the Ursa's turret is much better.
Only one warning; the Ursa is the biggest ship in the game.
This topic should help you understand the size differances.
The first picture (from left to right)
Boeing 747
Stack 1: Ursa, Medusa, Artemis, Zeus
Stack 2: Hercules Mk1, Apollo, Perseus, Ulysses
The second picture includes a GTC Fenris cruiser.