Some guy on FredMiranda did a huge study in which people put their cameras on manual, and shot a series of pictures of a wall, adjusting exposure by 1/3 of a stop, and the dynamic range was determined to be the number of stops between the lowest and highest exposure setting where there was recognizable detail.
The average was something like 7 2/3 stops, and some people (mainly with full frame cameras) reported over 9 stops. I'm sure some of this DR is not necessarily useful DR, like the bottom 1 stop and the top ~ 1/2 stop. But still, that's a pretty good DR. Part of the problem is that there is no shoulder, though, so highlights end up being all weighted equally until they cut out. So the DR is qualitatively different than on film.
I haven't studied this formally, but I'd give Velvia maybe 4 useful stops in my experience, and Astia maybe 6 or 7. I definitely have to be more careful these days shooting slide film than I ever did when I predominantly shot digital. Then again I could shoot 800 pictures to make sure I hit the exposure on one of them, and I'm not doing that with 8x10 slide film.