I am thinking of putting 6" components in the doors and 5 1/4" components in the rear deck. The rear are just for fill right? I am going to use subs in this system. Would this be a good plan? my bonne is a '90 in case it matters... Also I am going to build sealed enclosures for the 6" and 5 1/4" .

I'd say keep the 6x9'* in the back. They'll bridge the gap between 6" and 10 or 12" for frequency range.

i think most 5 1/4'* are sharper.......but thats my opinion

it really depends on which speakers you get. What is your budget. do you plan on buying something from best buy or somewhere like that or what.

I already have rockford FNX2514 5 1/4" components in the front doors. I want to get the 6" version of these speakers so they will be voice-matched. They are in small sealed enclosures. Would putting in 6" mids instead of 5 1/4 make a big difference? I am pretty sure i can get the 6" speakers for cheap. I want to avoid buying new 6x9s, but don't components give you better SQ?

Maybe you should consider a midbass speaker. Check out rockford'* component line and see if they have a dedicated midbass and not just a bigger midrange. either way you should get more bass out of a bigger speaker, but how much more bass just depends on a lot of other things.

The way I am thinking is that the subs are good up till about 70 hz and the 6" mid woofers would be effective down to about 60hz. Would I be better off putting the bigger speakers in the front doors instead of the rear deck? That way the front soundstage would be better.

The way my bro has it setup on his car.. he has a 8" under the center console ( the dead space between driver side and passenger side floor ) and also 6" on the kick area.. and that surely pulls the bass out to the front.. while the rear 12" does it job..

I doubt that any 6 can go down to 60 hz accurately. If you want something that will actually fill in the freaquency gap, you can go with adire koda 6 midbasses. they can accurately go down to about 70 hz until the sound really starts to cut off. But i still have mine cut off at 80.