Think I answerred my own question, found this good article:
Connected my Macbook via cable to Airport Extreme (Network Utility on Mac) showed Gigabit Connection. I also disable Wireless on Macbook to ensure LAN cable was being used!
The Airport Extreme is connected by cable to Time Capsule.
I did some rough timings of copied files from the Macbook to the Time Capsule (via Airport Extreme) and with my calculations using link above was getting transfer rates between 300 and 400 Megabits per second. So clearly shows connection all the way through is higher than theoretical maximum 100T (100 Megabits per second), so connection must be 1000T Gigabit between Airport Extreme and Time Capsule. I guess the disk speeds are the limiting factor here and why I am not seeing closer to the theoretical maximum of 1000 Megabits per second).
So good news, but it would be nice if the Aiport Utility could show the actual Airport LAN connection speeds like Network Utility does on the Macbook.