I saw that to last weekend. He had some good airguns on that stall.
It brought back many memories. I bought one in the States in 1979 and brought it back to the UK. I remember they didn't appear as official imports until later that year and were restricted however mine was not much more powerful than my Meteor and Mercury I had at the time.
In my AGW from 1983 the one on test gave 568fps with 13.5 grain Kassnar pellet ( never heard of them either). That was with 10 pumps.
Hope that is of some use.