I've never had one, nor most likely will ever have one. However, I've been fond of these one since the first ones appeared:
Penske IROC cars were 1974 3.0 911RSR's. One of the rarest modern-day Porsche's. The 1988 911 is a really really nice car! It makes the right noises, has the Porsche smell, etc.
Forgot to mention the 906 and 910! I saw Bobby Rahal and his Dad race different iterations at Mid Ohio vintage races. The 906 is simply understated excellence. I would luv to have the over the road edition of the 906