Just to add a little information:
There is a lot of water pouring in these doors. I checked all four doors with the door cards off and a hose draped over the roof - it look like I had hung the hose off in the door.
If you build custom mounts, you'll want to use plastic (stacked cutting boards will work) baffles/mounts and fabricate a water shield. I was going to go this route and after checking fitment of a driver with 146mm cut out and 73mm depth, which would barely clear the window and door card with careful placement, I decided to look for the largest cone area and x-max driver I could find that would fit the stock mount. I figured if I wasn't happy, I could always fall back on the custom mount and shield.
If you want to stick with the factory mounts with the water deflectors (like I did), you'll need to go with a speaker with less than a 133mm or 5.25" cutout. You’ll find that hardly any of the higher end true to 6.5” size speakers will fit. However, there are a number of popular so called 6.5” speakers that will fit like the Polk Audio MMs and Dbs, JL Audio C3-600, and the Infinity Kappa 60.11cs and JBL P660c speakers. The Infinity and JBL utilize the plus one woofer with a cone area (Sd) of 133cm2, but I believe the Xmax is 3.4mm and they have a rather high Fs of 76Hz - higher than most “high end” 5.25” woofers. This means with any real power, these woofers would need to be crossed higher than the size of the cone area would lead you to believe. So, while there are decent speakers that will fit, there are practically no “high-end” so called 6.5” speakers that will fit the stock mount.
At the time I made my speaker selection, the largest “semi-high-end” speaker I could find was the Alpine SPX-17PRO woofers. They have a Fs of 45Hz and the largest area (Sd - 133cm2) and throw (6.3mm - Xmax) that I could find - Xmax for most 6" and 6.5" car speakers are around 3mm. The 17PROs are a little veiled compared to my “go to” car driver (7” Vifa MG series) but most are – plus they sounded better than anything else I tested that would fit the stock mounts. Other drivers that I did not order, but considered trying were the $105 each SEAS Prestige L16RNX 6" aluminum cone woofer (H1488-04) with a Fs 39Hz, Sd of 104 cm2, and 6mm Xmax (126mm cut out, 70.5mm deep) and the $213 each Scanspeak 15W/4531G Revelator 5.5", 4 ohm woofer with a Fs of 40Hz, Sd of 95 cm2, and 6.5mm Xmax (125mm cutout and 71.2mm deep). The 17Pro is a tight fit (the mount needed a few passes of a sanding roll), so I believe the Seas H1488 or the Scanspeak 5.5” Revelator might actually produce more bass with the extra breathing room they would have around the mount opening. I know that the ScanSpeak Revelator is one of the best drivers money can buy – excellent extension and very low harmonic distortion.
Anyway, the long story short is to make sure you check the cut out diameter of the woofer if you’re running the stock mounts!
I removed my stock subwoofers while doing the remote entry antenna mod, and it dramatically improved the sound of my 2 12" subwoofers. Also I know some guys have replaced the stock subwoofers and running free air replacements. Take the time and add a decent aftermarket amp and build enclosures for the 8" subwoofers. With the battery being in the trunk and getting signal from the stock amp, this car is about the easiest to upgraded with subwoofers. I am still running the stock door speaker but added a audiocontrol line driver to run the 4 channel amplifier and mono sub amp. Depending on your budget and type of music you listen to the stock door speakers are more than ample, just need more bottom end.