imagine you have an alarm also? and you're not going to be running your system at full blast for extended periods of time with the engine switched off?
You'd get away with a 500cca lead type battery ... i had a similar setup in my previous beast (kicker 354xi amp, 12" rockford, stacker/hu, a few electronic gizmos) and i ran a similar battery without ever any startup problems.
The main reasons why you'd want to step up to a gel cell or fully sealed system are:
- often are deep cycle
- don't leak gas
- no maintenence
- can relocate into the boot
- often can be smaller than factory battery (talking only about the optimas and odysseys here)
- greater cranking capacity
downsides are of course ... cost.
Hope this helps you.
edit> in summary... don't be tight.. go the > 500cca lead-acid as bare minimum, go the gel cell if you need that overhead.