I was wondering if I should stick with 6x9s in the front and 6-1/2s in the back, or should I go 6-1/2 all the way around? Opinions?

 

I've always found it best to have the same size all around, because when you have different sizes the music sounds a little different and doesn't sound perfect. When you're dropping the $$$ on a new system you want it to be perfect so I'd stick with the same size. However if you do decide to go with different sizes, make sure it comes from the same brand.

What brand speakers are you looking at?

 

6x9 have a better bass sound, that may be why the front doors are bigger than the rears.

 

I'd be very surprised if you could tell quality diffrences between 6x9 coax and 6.5 coax. now, 6.5's give you more versatility because they come in componet stylew ith seperate tweeters, but 6x9's will have more bass.More woofer surface are means more bass. If our looking for an easy install, your better off sticking with 6x9 up front and 6.5 out back. Same manufacturer is reccomended on basis installs.
I had a set of Polk DB series coax's and they sounded really goood. They were pretty cheap too.
coaxial=2-way or 3-way
component=individual woofers and seperate tweeters w/crossover

 

I've got the Polk DB series as well and they sound great, have no bass but the highs couldn't sound any crisper. The rears are actually 5.25 but 6.5 will fit. I'd go with 6x9s up front due to the easier install and cheaper since you don't have to get the 6.5 mounting brackets. I will say this though having the 6.5 all around and having a quad cab the back seat was completely overpowered, what sounded like a good volume up front was deafening in the rear so I had to lower the amount of volume for the rears to make it even throughout the cab.

 

I am going with type-R speakers and I'm building a custom enclosure for an Fi Q 12 sub. I just didn't know which way to go with the door speakers