The SAN has other disks and also spares etc. The 10 disks I am talking about are available for dedicated use for this sql server.

I would certainly like to have more disks available, but given the constraints the question really was whether anyone had experience of whether SQL Server performed better with disk arrays dedicated for purpose i.e. separate database, logs & backup disk arrays where each disk array has few spindles (e.g. 2 in my case) versus a disk array with more spindles (e.g. 9 in my case) but with all the disk activity going to the same array. So I'm looking just at performance in this case as with either configuration I have redundancy to cope with a failed drive.

I may be able to test this myself soon when I reconfigure my Test environment.