It doesn't matter, the best units won't put out much more than double the power of yours, double the power= 3db more sound, 3db is considered a slight(barely audible) increase in volume.
So if you find the most efficient speakers that sound nice it may play louder than inefficient speakers on a powerful HU, hope that make sense.
My POS has over 500W RMS just for the front speakers but it won't play much more than double the volume of a normal HU powered system, had to jump start it yesterday because of my stupid stereo.
Since you seem to be the car audio guru round these parts, I'll direct this your way (but if anyone else has something to add feel free):
Trying to plan out a sound system for the esky. Right now its just got the stock AM radio so it's pretty much a start from scratch deal. I'm after good sound quality rather than massive volume levels, but it'll still get a share of the clockwise twist.
Starting with the head unit, is Alpine still the way to go? I'm hesitant to go for anything Kenwood/ Pioneer/ Clarion etc. and Alpine is the only brand I know of thatn seems to get the consistant thumbs up.
Onto the speakers, I've been thinking that 6.5" splits all round might be the go this time round, after hearing from a few people that 6x9's don't really offer good sound. Any reason why not? Have any experience with Hertz gear?
The boot is surprisingly big, so I reckon I could fit one or possibly two 12" subs (or 10's. any reason to go 10's over 12's except for space?) in there with realtive ease. Again what brands should I be looking at?
As far as amps go, does branding really matter as much? I assume it's still a good idea to steer clear of Fusion/ Jensen but so long as you can match the RMS power requirements then it should be right, yes?
Don't want to spend a fortune, was hoping for ~$150 per pair of splits, ~$200 for the head unit, ~$500 for a sub/ amp combo and ~$150 for a 4 channel amp. Obviously willing to spend a bit extra if the gains are worth it, but after $1k it turns into a diminishing returns senario from what I've heard. These are all second hand/ ebay prices, not keen to pay retail.
Out of curiosity Fairy, what gear are you currently running?