I used to have two ways in the front and three ways in the rear of my Integra, then later in my first RX. The difference in the sound of the two was noticable, but nothing special.

I've since past my sound system days, though. I used to have in the Integra:
pioneer DEH-4300 head
two 6.5" pioneer two ways in front
two 6.5" pioneer two ways in rear
760W Sony two channel amp
two 12" pioneer 450W subs in back

it sounded so sweet, but the sub box was just soo heavy. Now I have:
pioneer DEH-4300 head
no front speakers
el-cheapo 6.5" two way rear speakers
It puts out just enough sound to keep me from going nuts from the exhaust tone.

Remember, if you plan on going fast, an extra 80 pounds of dead weight stereo isn't helping anything, esp. in a pudgy del Sol. If you ever plan to keep up with your brother and I, a sound system beyond a decent head and a few speakers isn't something to put money into. I am still trying to find a lightweight way to mount the subs in my new RX... but that's something else. Speed is the priority, and the old sub box noticably impacted acceleration and cornering ability.

Note: nothing against the audiophiles of the site, I know this guy personally and am commenting as such.