Rate of fire is the same, but energy use seems constant per gun fired. On Medium level, a a Tauret with no energy directed to weapons can fire off 41 shots from double Kaysers, 20 from quad Kaysers.
2+2 guns provide as much firepower as one 3-gun bank. This makes linked fire a valid choice if you don't need the flexibility of varied guns, but inferior to having all guns in a single bank.
4+2 arrangements favour varied loadouts. Firing all (identical) guns will result in the same firepower and energy usage as only using the 4-gun-bank. 4 anti-fighter guns and 2 Maxims seem the obvious combination.
4+4 guns seems wasted potential when split. An Erinyes can't support 4 Maxims well while 8 of a kind works well for any dogfighting weapon
With Subachs, you have firepower not much below quad Kaysers at a fraction of the energy demand.
With Prometheus S you have a snipers' dream - blowing up brombers going head to head has never been so easy.
With Kaysers, you have the close-range firepower to kill any fighter-sized target in seconds without using Tempests.