I can tell you that I have 6.5 inch Alpine type S Components in one of my miatas and I love them. The 6.5s fit just fine, but installing the tweeter was a little bit of work. I had to use a hole saw to make room for the back, but the results look factory. I do use a amp with these speakers, and the results are music that can overcome the wind noise on the highway with the top down, and enough midbass that will shake the rearview mirror if I want.
I'm using Kenwood 6.5 three ways, they sound decent some bass, not enough to destroy anything, but thats not expected from 6.5's anyway. They are running from a regular Kenwood headunit. I'm sure with an amp the output could be raised significantly, but i dont want to have to worry about mounting and such. I would suggest going with any decent 6.5 two or three-way speaker so as to keep the install simple. A trip to your local "Best buy" or somthing similar should give you the options that you desire. I think the key is to hear a few different speakers and then decide what works for you. And for better prices i suggest going online. Or possibly PM me with the model number you like and i will try and find you a good price on it.
I think the best balance of cost/sound/packaging is some 6.5" Focal coaxials powered by a small 2-channel amplifier pushing 75-100W RMS. I picked up the Focals on eBay for cheap and power them with a compact Soundstream amp. They play loud and clear and sound really good especially when tweaked with my Soundstream EQ.
5x10??? THAT is new size for me. (I would have to guess its a typo...)
Speakers are VERY personal in nature, as what each person hears differs in reality. 2 people can listed to the same thing, but here it (tonaly) a bit different. So, a speaker that sounds good to me, might onky sound ok to someone else.
There are a TON of choices in the $80-100 range for a good coxial speaker. Under $100, and you can usually "get away" with running them off headunit power. Anything more than that in the price range ($150-300), and you are eeking into territory where the speaker will sound a LOT better with a small amplifier (50-75 watts per cahnnel).
Lots of choices....
I like the Polk SR speakers that I have in myc ar now, but will be changing to a set of Hybrid Audio Technologies (www.hybrid-audio.com) speakers in the near future.
I have Polk 6.75" in my doors. They fit with a little persuasion to the sheet metal in the door. You probably only have to shave about .125 for the diameter. So buzzing around it with the dremel tool is quick. I took the grates that came with it, screwed it on the plastic covers, had to trim the back of the plastic panel to accomodate the larger speaker, but it looks and sounds awesome. here's a pic:
I highly recommend the Infinity "Reference" series of speakers . I worked at both Circuit City and Best Buy for a while so I have a lot of experience with speakers in this price range ($35-85/pr) and to my ears the Infinity beat every one of them by a pretty impressive margin . For the price they can't be beat .