So I have six 6-600 APs running in unleashed mode and so far very happy with the performance. I have them in a small 44 unit hotel, and since the day I put them in, have had nothing but compliments about the wifi!
I also have an older ZD1100 sitting idle. I'm wondering if it would be worth it to get the license renewed and if using it to manage the AP's would add much in terms of functionality, as opposed to what I have now.
With R600's I wouldn't recommend a ZD1100 as your very limited on the firmware versions you can run and the ZD1100 is end of life, you may not be able to purchase licensing at this point. I have the ZD1200 and like it better than Unleashed. There is no way I'd consider a ZD1100 to manage your R600's.