I have a 500 Dressage. I bought it because I only had a close contact saddle for one of my horses and wanted something slightly more secure but still practical for my young horse back then. I still have my 500 and ended up selling my close contact.
I really like the 500 because is versatile and looks nice. I've ridden a fair bit in the Isabel, and I can see its appeal, but personally I did not like it at all. I just never felt comfy in it, but it does has a deeper seat. I don't the fake suede, or real suede, so that would also contribute to it. Also, I don't think the Isabel would as good as a 500 in a show ring, although neither would be ideal. I have never ridden in a 2000 Dressage but I rode an all purpose, but was not that keen on the suede stuff.
I have Cair, and I don't know if I would buy a non bates saddle because I love having Cair. My saddle fits pretty much every horse which is great for me as I occasionally ride different horses. I've had flocking saddles before and I feel that you have to get the them re stuffed (or whatever its called) 2 - 4 times a year, especially if the horse goes in and out of work. I did mine every season cos my horse changed body shape. Here that costs 150 for a good one, so its adds up very quickly. I have had problems with horses whose backs had been ruined by saddles and it took a lot to get them moving properly again. If you are going to get a flock saddle make sure that you fit it. I would definitely recommend Cair.
I haven't really noticed the squeaking much.