Hi,
I guess noone is gonna offically tell you that some of the versions are not stable. I have general rule to avaid FCS releases and short term releases, so for example in case of CUCM 10.0 and 11.0 I would not install, same as all the FCS 11.0.1.10000-10.
Usually if version has release around SU3 - SU4, it should have all stability issues and major defects fixed. And it would usually be around 6-8 months on the market already, so it's tested by other customers :)
Leszek