IMHO if you are going to upgrade the upgrade the tweeter you should think about just going with a component speaker set and replace the woofer in the door as well. All speakers work best within a certain frequency range (I.E. 5kHz - 20kHz), The matched woofer and matched crossover network is the other half of the equation to making it sound the best it can. doing a component set can save you money in the long run also, here is an example from woofers Ect.Alpine SPS-1005 3/8" tweeters = $49.99http://
www.woofersetc.com/p345...r.htmAlpine SPS-600C 6.5" component set = $89.99http://
www.woofersetc.com/p626...m.htmWith the later not only are you getting a bigger tweeter 1" as opposed to the 3/8" it will also handle more power and the component set also has a built in crossover where as the Alpine tweeters by them self don't include crossovers.The added benefit of doing a new mid at the same time will yield you probably a little better mid bass and some smoother vocals. I am not sure what the frequency response of the factory woofer is, but that would be needed to suggest a tweeter that will best fit what you are looking for.