Yep.. they sound good but I personally couldn't get on with them though with the 12" MG's. Why?... VFM didn't seem to balance. I paid something like £700 for them and I've not missed them.
As been said before, ST's are a 'suck it and see' kinda thing.
I had the ST200's too. They are very cute things I must admit.
I do like ST's, and I really liked them in the Harby SHL5's and the Dali Helicon 800 MKII's (although they were ribbon, much nicer, smoother sound me thinks)... Dunno, maybe they worked better for me in the staggered driver configuration rather than a DC.
btw.. Andrew... have you sorted your cabs yet? - If not then that is where the effort should go in to IMO and not Supertweeters.