The speakers in the Infinity system are 8 ohm. You're going to be disappointed in your sound if you are only replacing factory speakers with aftermarket. I just went through this recently. I worked with Crutchfield to find something that would fit my front door factory 6x9 speaker locations, and they warned me ahead of time that nothing I was going to put in the factory speaker location with the factory head unit / amp was going to give me the same bass response as the factory system. I didn't listen and went through a couple of speakers trying to find something that would work.
First, you are limited because of the mounting depth. You aren't going to find 6x9's to replace the factory ones that will fit because of depth. If you go with a 5 1/4" , 6 1/2", etc... you aren't going to get the bass out of them that you would with the factory speakers. It's frustrating. The factory speakers are cheap paper cones that distort really easily. I ended up blowing mine up, so I needed replacements. When all replacements failed, I called Dodge. Wow. Sticker shock. They want more "per speaker" than you would pay for almost all aftermarket pairs of speakers.
In the end, my choices were:
1) Live with the reduced bass, but slightly cleaner sound of the aftermarket (which I did)
2) Go with factory. Yech.
3) Rewire and go with an external amp, new speakers, probably a new head unit, etc... I passed on that. $$$$ + I'm getting older and grouchy.

In my younger years, this would have been the route I went.
Hope you find something you like, but I can almost 100% guarantee you that you will NOT like the sound if you simply replace the dash and front door speakers. You won't get the bass, and you won't get clear mids. It's going to be muddy and weak.
All the best,
Glenn