if your planning on a stereo that large and requiring an optima calcium cell battery, maybe getting a 100amp alternator is a good idea as well, just means that your not always relying on your battery so much.
it means that if you reach the limit of the alternator (standard is 80amp) for pumping out to ancillaries you will not have to run down your battery....just a thought... i know a lot of 4wder's who run a larger alternator because they run a lot of extras and it just saves you having a battery run flat..and large stereos tend to require a large amount of POWER..
To help with light dimming with bass try doing the Big 3 upgrade first. Basically upgrade the alternator to battery, the battery to chassis, and the battery to engine wires. Then get a D34. Then look at a bigger alternator.
Just go for the optima. Mine starts everytime and I only drive it once a month or so. Takes a half hour drive to fully charge it from flat. I can watch dvd's wth sound through the stereo for an hour at a time without a problem.