しかも is pretty straight forward:
Let's go get lunch at Ichiban next time. The food is great, also the servings are big.
My kid is a genius. He's great at playing the piano. What's more, last month he passed the 2nd grade of the Eiken.
I think of しかも as 'Also', 'What's more', or 'On top of that'.
The thing is I don't see how that is more different than それどころか. For example:
I had a oyako-don at the dining hall and it was terrible. To begin with, the meat wasn't cooked properly, what's more, there wasn't a lot of rice.
I have a feeling that the translation of the two phrases is not going to change very much when put into English, but that is not really important. What I want to know is the correct time to use each respective phrase. Or, are they not as interchangeable as I am thinking?