cd's/SACDS to test highs?

Use regular music to test your speakers. Listen to how well the ribbon tweeters integrate with the other driver(s). The high frequency range of the ribbon tweeters should be smooth and continuous with the rest of the frequency range of your speakers.

I own a pair of speakers with extended range ribbon super tweeters and was cautioned by the manufacturer not to use high level high frequency test tones with them as you can easily damage the ribbon tweeters that way.

There is a song on Moody Blues "Days of Future Passed" that has probably one of the highest notes that I've heard in a song. I believe it is "Evening Time to Get Away". It floats back and forth between the right and left speaker a couple times throughout the song. I only have it on vinyl. I can only imagine what the SACD would be like. The ribbons on my Infinity speakers throw that note out like its coming from behind the listener.
Have fun, JD

Not sure what genre you're into, but there is an incredibly beautiful "classical song', with very high female vocals (but not opera style) interplaying with a violin (Gidon Kremer), on the Arvo Part album "Arbos". The song is called "es sang for langen Jahren". This is another staple recording of mine to evauate "highs".

I would use one of the early Nora Jones records. The vocals are very up front and on a good system, you can actually hear the sound of her mouth opening, and the breath sounds. On a poor system, you will either lose these things or the vocals will sound harsh, but on a good system, she sounds like she's in the room. BTW, the music was good on the first two records, as Nora wrote very few of the songs. She's a decent enough singer, but her writing is for shit.

On CD look for Vaughan Williams the Lark Ascending with Iona Brown on violin and Neville Marriner conducting. The finest semi-quavers I have heard yet and a brilliant recording for violin.