Wattage is just one measure of energy consumption. Does not necessarily translate into more wattage=louder.
I have, for example, a pidly little 40 Watt tube amp with a 10" speaker for my guitar amp, and I will make your ears bleed almost, thing has no problems keeping up with 200+ watt amps.
There's RMS vs peak wattage to account for, and the efficiency of the speakers to produce more sound. Matching up your impedance for the overall speaker package to get your best sound quality and "loudness" will get you much further than just looking at wattage alone.
Best investment is good efficient (look at the numbers for frequency response, etc) speakers designed for the sound range you are looking for, and use active cross overs to cut the sound from them that is out of their range or undesirable.
Sometimes you get what you pay for, sometimes you are paying for a name stamped on the plate.
so i finally finished striping all the speakers and wires out of my dads accord, got lots of goodies out of it... although i did realize his amps are all ****. and they will be the first things i upgrade. he has two 1000 watt subs powered off of a 160 watt 2 channel RF amp. and his other two are both 2 channel and 50 watts a channel... witch i dont get bc his car hit hard as hell and was loud and clear even though the severe lack of power the subs were getting like 1/8th of their max, and the interior speakers were geting only 1/5 of what they can handle, will have to wait and see i wont be spending anymore money on it till after it gets registered and stuff, install coming tomorrow and a picture or two coming an a few minutes