I put some Roush spring on my SVT using the original struts last August. I was somewhere around 40K on the struts then, now about to hit 49K. They are noticably stiffer than the stock springs, but all the body roll and nose dive are long gone.
Rough roads are a little bumpier. Uneven pavement (asphault road to concrete overpasses) is jarring, but tolerable.
If I had it to do all over again, I definitely would. My struts seems fine except with 4 people in the car it gets a little bouncy, but with just me (95% of my driving) no problems at all. I have a new set of ST200 struts I bought when BAT had them for $150, but see no reason to put them on yet.
Keep in mind though, determining if ride quality is too stiff is really quite subjective. One person would think it's fine and another person will hate it - so pick your passengers carefully.