Hmmm... I think you're talking about the Prothane total kits...
If that's it then that's what I'd go with. I can't think of a reason why you'd want them to all be rubber with exception of the upper control arm bushings.
I have been thinking of doing a complete urethane bushing kit. What are your concerns about the harder bushing? My stang has 177xxx mi. and could benifit from some new bushings and I have never had the luxury of comparing it to a stang with a "tighter" suspension or anything with urethane bushings. Just wondering.....
Never seen a replacement rubber kit either. Energy Suspension's bushings are supposedly softer than the ones offered by Prothane, but they're both harsher than the OEM rubber.