We used AO for the past few years but this year we're using SCM as our main history study, with some AO books (natural history selections, nature readers, Foster books) included in their reading. I had thought for a while about doing AO and SCM, and while this could be doable for us, as my dh works 2nd shift and I could technically do a normal AO school day and then in the evenings, instead of t.v., etc, we could do our SCM study. But that is quite a bit to keep up with and I was concerned that something would not be given the time it deserves.
::shrug:: It's a tough call. I really do enjoy both programs for their own unique strengths. If you can fit them both in, go for it! They're both pretty great. Then again, sometimes less is more. Yeah, so I'm no help at all.
I hope it all comes together for you!