your car is one hell of a lot quieter than a midyear so i don't think you need that much power....here's the general advice i was given years ago about buying stereos and i think this works for any audio system...
first, buy the best speakers that you can afford, doing that by either reading reviews or by listening to them (preferably the latter)...once you pick your speakers, you know which size (wattage) head unit to get...in my opinion, and based solely on my own hearing, the biggest problem i have with speakers is a "muddy" low end (bass) which masks the other notes for me....good quality low cost multicomponent speakers are available now so that removes a LOT of the problems but if i have space in a vehicle, a really good investment is a subwoofer, mostly because you have the capability to bleed off the low frequencies which cause the maximum movement of the speaker cone to a speaker which is set up to handle it..
just my .02 and good luck