Donnington is on my wish list and I will do it next year.
Trackdays are invaluable experience giving so much information on what the bike is capable of, even the fazer!
With regards to old slower bikes in the fast group, although being overtaken frequently if you were able to watch them properly the chances are they were going the same speed round the corners as the fast sports bikes, its more at this point that there is a difference between the groups and was my biggest annoyance when I did Bedford autodrome, because of my lack of experience on paper (only 2 trackdays previous) I was put into the novice group, my braking points were way later than 95% of the group and my corner speed was in my belief higher than everyone.
Funny thing is that both of my previous trackdays I booked into the intermediate group and it was never questioned or changed, and in that group I was going around the outside of people at Rockingham!
Good write up Si, although its natural to be a bit jittery about the day people need to realise that its a good safe day out, and ultimately will improve everyone's riding ability!