From what I was told at Best Buy when I went to replace all my speakers is that 3 way speakers are more bass heavy.
I'm assuming that the Firebird and Camaro hatch sizes are the same, so from what the installers at Best Buy told me is that 4" were the biggest you could go in the hatch. Anything bigger is too deep. With that said, there were only 2-way 4"s at Best Buy, so that's what I went with. This is what I have in my car:
1 Pioneer deck: DEH-1200mp
2 6-1/2" Speakers- TS-A1673R (3-way speakers)
2 4" Speakers- TS-G1043R
Not really sure how much better these are compared to stock since the stock speakers I had were shitty. The factory CD player was skipping every time I hit a bump and scratched my CDs. My friend said his Grand Am GT did the same thing, so I went to buy a new deck. They had a special that if you buy the same name brand of deck, speakers, and installation, you would get $100 off. So I spent $300 including installation. Next I want to get new subs, since right now the stock subs sound like absolute shit on most of my songs and the mid and high range hit harder than the low. Other than that, they sound great without bass. When I turn the bass up, the panels start to rattle.
Not really sure if it had anything to do with it, but my friend bought rockford 6x9s, or somthing like that, and they were 3-way speakers. He was told to not play his music loud for a few weeks so the speakers would break in. I wasn't aware of this, so I never really took it too softly on my speakers. Not sure if that's why the bass doesn't sound too great, or if it is really just because of the stock subwoofers.
Whenever we roll in his car with only the rockford speakers, his car's bass seems to hit way harder than mine when he turns it up all the way and I leave mine at neutral. He also has a GTP with the stock sound system and 2 12inches. With the bass turned all the way down, it still bumps harder than mine at neutral. I tend to leave the bass level on neutral since it doesn't sound like absolute shit, and it bumps decently. It might also be just because I listen to my iPod through the sound jacks.