Help Please!

I want to replace my factory speakers with aftermarket and add a amp and sub. There are so many choices out there. However, the more I read the more confused I become. My goal for this upgrade is sound quality not loudness.
Speaker Size. I have used online sources to get sizes and I get 5 1/4 and 6 X 8's. I call local installers and they say 5 X 7'. Does anyone know the answer?
I have chosen to go with a 5-channel Alpine MRV-F450 amp. I have read good reviews on it for sound clarity. And it should be able to power both my speakers and my sub. I have also chosen an Alpine SWR-1021D Subwoofer. As for speakers, I was trying to go with the Infinity Kappa 63.5 I 3-way speakers for the four doors. Do these sound like good choices and will those speakers fit my 2001 supercrew without too much adjusting? Also, I read that the Front speakers are the most important and the back speaker don't matter as Much.

Thanks, any help with matter would be greatly appreciated.

 

The 6x8's and 5x7's can be used interchangeably(is that a word?). Lots of people here also use the rounds, which fit fine in the oval holes!

 

The actual holes are 6x8 size. Most if not all 5x7s have additional screw tabs that line up with 6x8 holes. I had Polk EX 368 (true 6x8s) in my front doors and they sounded great until I blew one. I now have Adire Koda Components with 6.5 inch mids. I made a wood plate to adapt them. They sound even better than the Polks. More midbass.

Rest is in sig:

 

if i were you i would check out the jl audio xr 5X7s. i have a pair of them powered by a jl 300/2. ive been through many-a-system and they sound the best by far. check em out!!