In my humble opinion, the Penske's are a great race shock but not such a good shock for the street. They are designed to be rebuild-able and they can be re-valved, etc. Also, for many years it was the upgrade shock of choice for the GTs - when there were few, if any, non-OEM choices available. For track use - properly valved (which most were for the GT) they are wonderful.
On the downside, we had MANY owners complain of clunks and squeaks from this set-up and several thought they were a bit harsh. Several of the Penske owners "upgraded" to the Ohlins (like Vince commented above) which, IMO, is a no-compromise shock.... but the price is not for the timid.