OK I am not sure this is since the update to 6.10.x but I have just noticed that the speeds writing to my array have fallen from 130-140 MB/s down to 30-40 MB/s.
The other odd thing I have noticed is regardless of the 'Tunable (md_write_method)' setting is, it treats it as if it is on reconstruct write. Although this is the setting I usually have it on the speeds have dropped and if I set it back to Auto it still reads all the disks when performing a write as if it set to reconstruct write.