The message that 6.6.5 is the new update should be for all those who use a version prior. I have used 6.1.2 for over two years now, and I am not budging.
My guess is you would need to be on 8.2 to get ICD-10 support. I like the ICD-10 in AC, but I don't like waiting 15 to 20 seconds to open eRx.
I don't use AC for anything billing so I am not budging until this is fixed.