The set is 5i-SW with no pitch. He didn't tell me anything about them, but I'd love to find out what I can.
I think if you google Ping Zing Karsten irons, you should be able to get some good info on them. I've seen some sets on ebay, and for older irons, they fetch a decent price for their age compared to most older irons..
Good clubs, perfectly playable, but a sales disaster for Ping when they first introduced them. A radical look and departure from the popular Eye2 clubs that they were to designed to replace. Ping quickly switched to the Zing 2 the following year, and to the more Eye2-like ISI irons after that. Looks like your set is in pretty good shape. I'd hit 'em!