The best thing in the world (resulting in crushing your enemies, seeing them driven before you, hear the lamentation of their spouses...) is large volleys consisting of single missile salvos.
Examples are fighter (on 8k techs + Ion Drive and Box launcher), but the concepts work for full-size warships too.
Quasimodo class Fighter-bomber 300 tons 5 Crew 51.2 BP TCS 6 TH 14 EM 0
2333 km/s Armour 1-3 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 0 PPV 1.8
Maint Life 8.89 Years MSP 11 AFR 7% IFR 0.1% 1YR 0 5YR 4 Max Repair 21 MSP
Intended Deployment Time: 15 months Spare Berths 1
Magazine 12
7.2 EP Ion Drive (2) Power 7.2 Fuel Use 16.57% Signature 7.2 Exp 6%
Fuel Capacity 15 000 Litres Range 54.3 billion km (269 days at full power)
Size 3 Box Launcher (1) Missile Size 3 Hangar Reload 22.5 minutes MF Reload 3.7 hours
Size 4 Box Launcher (1) Missile Size 4 Hangar Reload 30 minutes MF Reload 5 hours
Size 5 Box Launcher (1) Missile Size 5 Hangar Reload 37.5 minutes MF Reload 6.2 hours
Missile Fire Control FC75-R120 (1) Range 75.9m km Resolution 120
ASM-3 (1) Speed: 22 600 km/s End: 57.9m Range: 78.5m km WH: 4 Size: 3 TH: 158/95/47
ASM-4 (1) Speed: 22 600 km/s End: 57.9m Range: 78.5m km WH: 6 Size: 4 TH: 150/90/45
ASM-5 (1) Speed: 22 600 km/s End: 56.6m Range: 76.7m km WH: 9 Size: 5 TH: 128/76/38
Missile to hit chances are vs targets moving at 3000 km/s, 5000 km/s and 10,000 km/s
This design is classed as a Fighter for production, combat and maintenance purposes
3 box launchers of different sizes launching missiles of identical speed means that we get 3 single-missile salvos traveling together from a single fire control.
This particular deisgn sacrifices performance for endurance and ability to operate independently of carriers.
Tortoise class Interceptor 400 tons 7 Crew 90.8 BP TCS 8 TH 96 EM 0
12000 km/s Armour 1-4 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 0 PPV 1
Maint Life 0 Years MSP 0 AFR 80% IFR 1.1% 1YR 7 5YR 104 Max Repair 21 MSP
Intended Deployment Time: 0.3 months Spare Berths 0
Magazine 19
24 EP Ion Drive (4) Power 24 Fuel Use 336.02% Signature 24 Exp 20%
Fuel Capacity 15 000 Litres Range 2.0 billion km (46 hours at full power)
Size 1 Missile Launcher (1) Missile Size 1 Rate of Fire 10
Missile Fire Control FC75-R120 (1) Range 75.9m km Resolution 120
ASM-1s (19) Speed: 12 000 km/s End: 100.6m Range: 72.4m km WH: 2 Size: 1 TH: 80/48/24
Missile to hit chances are vs targets moving at 3000 km/s, 5000 km/s and 10,000 km/s
This design is classed as a Fighter for production, combat and maintenance purposes
This fighter can keep up with the (slow, high-yield) missiles it fires, the result being 19 1-missile salvos traveling in a single clump (on the condition that we fire as we approach the target at top speed). Unlike the design above, this can make us of collier variants to give us a very respectable amount of ordnance on limited tonnage.
This one is hangar-based, the high performance required simply isn't practical on a standalone craft.
With larger ships, we can circumvent the need for extreme ship speed by using two-stage missiles... the firing ship just needs to keep up with the slow cruising stage.