I tried many old mirror lenses, and was disappointed by most, including an expensive Contax Zeiss 500/8 apparently in perfect condition (I wonder...).
The only one I could get really good photos - and many rejects due to difficulty to focus - was the Tamron 350/5.6 SP.
Did some of you compare mirror lenses of yesterday (say, pre-1990) with more modern ones (say, post-2010)? If yes, what did you find in terms of I.Q.?