I put heavy duty Bilsteins all around on my '92 Mustang convertible about 8 years ago and they've been tremendous. As firm today as when new. Very stiff. If you like a nice, tight ride then you'll like these.
I got HD's on my truck and love them. Firm yet rides much better than the Monroe crap. Good shocks from a good name (Bilstein, Koni etc) are worth the money.