Hi Umbrian,
If you do get a Salvia 'Alan Chickering' or (one of?) the parent plant/s S clevelandii, do a lot of research on summer watering. I have managed to kill 3 in 3 consecutive years by giving them summer water in pots. This year I dug up my S. 'Anthony Parker', transferred that to a large pot and put S 'Alan Chickering' in its place. I will water it a little while it is still flowering. I have to say, though, it has never looked in need of water. It is next to an established oleander and myrtle so I only hope it gets roots down deep enough to compete with them over the summer.
If you have a choice between S 'Alan Chickering' and true S clevelandii I would go for the later. The perfume from the leaves filled the garden with the mot wonderful scent without needing to be rubbed. I could smell a small plant from several meters distance as I walked into the garden. S 'Alan Chickering' gives the same perfume but I find I have to run my hands over the leaves first.