The SEAS would be an excellent choice, though I believe their off-axis response isn't the best but it should do very well. I've also heard they are a laid back metal dome tweet, well, laid back for a metal dome anyway. May I suggest looking at the LPG 26na as well, it's what I use and also VERY laid back for a metal dome, in all honesty much softer to the ear than my old type X soft domes (non-ring radiator version).
The Peerless mids you're looking at would be an excellent choice as well. Peerless has always made great drivers, and their Exclusive line is no exception. The HDS mids that I'm currently using are more of a "value" version of the exclusive. Similar specs, and design, biggest differences are obviously the phase plug on the exclusive, and apparently the Exclusive also uses a bit more copper shorting rings in the motor to lower inductance. However, it was said to me, that the slightly lower inductance probably wouldn't make an audible difference while driving due to outside interference, IE wind and road noise.
Just thought I'd give you another option, I'm VERY happy with the drivers I chose, though I would have loved to pick up the Exclusives, I couldn't justify the slightly higher price for the difference in performance. Though I would still love to own a set regardless //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif.