Maybe you should do some more research. If you aren't happy with your stock setup, change it, but there is a LOT more to it than just swapping speakers. Here are some things you need to look at before you drop the money.
1) Your factory speaker locations are 6x8
2) Your factory speakers SUCK, they are a thin, non pressed paper cone and thin foam surrounds. Now that be said, there is NOTHING more efficient for the power off your stock headunit (or any unit) than the factory speakers.
3) Looking at a 4 way speaker, like the one above, will just divide up the power more-so than if it was just a regular coax 6x8.
Pretty much, I don't know what your goals are, but I've completely GUTTED my system, I had the stock Shaker500, now I have a Kenwood DDX-7019 touchscreen, 4 RF T1682c 6x8's in factory locations powered by a T400-4 amp, 2 P1 8" woofers in each door off of a T400-2 amp, the T1652-s 6.5" component set in custom kick panels, and two 10" DC XL's off of two RF T1500-1bd amps, plus a MechMan 270 amp alt, Optima Blue Top under the hood and an XS Power reserve battery in the spare tire well. I've completely ran through the car, albeit a 2006, but the stock speaker location, setup, and size is the same. I compete in SQL and SPL in MWSPL and USACi, so the car sees a LOT of audio judges and I've done just about everything in the car in seperate stages, so I can tell you what changes I've made that would meet your goals and keep you from wasting your money.
What you need to do is tell us WHAT you dislike about the stock setup (no mid-bass, no low-bass, dirty highs, low volume, distortion, etc. etc.) and what you would LIKE it to sound like and the type of music you listen to. I know I can, and I'm sure there are others on here that have blended performance and audio lol, help point you in the right direction for what you will need in order to get the result you want.