Free air resonance?

Does that mean that since I'm going from a tweeter with an fs of 1500 to an tweeter with a fs of 600 that it is a good thing? Do I have more versatility with the tweeter with the fs of 600? I ask because this is what I'm going to try.I'm going from the Hales Vifa (fs 1500) to the Seas Millenium(fs 600).

Hello Dr,
Would you then reccommend that I leave well enough alone? I should note that an amp designer (the one who designed my amp in fact) replaced his Hales T5's Vifa's with the same Millenium tweeter that I am going to get. He did remove the .33 ohm resistance from the crossovers tweeter section however but he was extremely pleased with the results. What I am saying is that I am not doing this blind but following the experience of a proffesional who had success with exactly the same upgrade. The only difference is that I redid my crossovers(with success) and he did not upgrade the crossovers. I did keep the Hales T5's crossover's design and kept all the origional values.

I put in the Millenium tweeters about 10 hours ago and am extremely impressed and excited. Perhaps my speakers won't read well on paper if tested, I don't know but the sound is more sophisticated sounding. It is not "dark" or have lower levels of high frequencies. If anything what's not there from the old tweeters shouldn't be there. In other words with my crossover mods my Hales tweeters were sounding a little harsh but acceptable. Know the sound is smoother and yet very detailed. A pluck of a bass string sounds ever more like a pluck from a bass string. Symbols and other high frequency sounds sound more natural, less hyped. Piano notes actually sound like a piano.
I am pleased. I hope I like how they burn in.
Thanks to everyone for all your help and advice.