I was in your same position back in the day. I even started on a 1k as well. Just ride your own ride, no one cares if you can or cant keep up it's not a competition. My first ride with these guys shocked me about how smooth and silky these guys are when they ride, not to mention the pace they ride for 2-3 hundred miles at a time lol. Oh, and I had them waiting at every stop, I was so slow they took turns sweeping me . After tens of thousands of miles on twisty roads, I'd like to think that I have some sort of pace, although admittedly I've slowed down on the street since I've gone to the track.
It motivated me to become a better rider so one day I could be like those guys. If you attend this ride I just ask you to do these things:
Ride your own ride, you will not get left behind or laughed at for the pace you feel comfortable with.
You have a great guy sweeping you, ask him the questions that you have.
Listen to the advice that is given. These guys know what they are talking about and have tens of thousands of miles running at "the pace".