I've ran every spec stage clutch in both of my mustangs (now with the Spec 3+) and I've never had a problem with spec. I'm going to try out that Twin disc spec next time around.
I've read a few people having problems with DFX's, thats why I stay away from them, along with spec's being so good to me. Their is tons of info on Mfords about people w/ problems using the DFX. I remember reading one problem with a user w/ a spec 3. Take that for what it's worth.
Kevin