There are samples of Miquon that would help you pick the right levels. My dd is only in Primary 2a, but I'll share how I combine the two.
Singapore is our primary curriculum and we chug along until we hit a brick wall. That is when I switch to Miquon.:lol: We play around with it for a few weeks, and then go back to Singapore. By then, she is usually ready to master what seemed too hard before. When she finishes a Singapore book, or is seeming bored by it, we switch to Miquon for a bit. She has done fractions and multiplication with Miquon, so that will be a piece of cake when we get to it in Singapore in a few weeks.
I do know there is a chart online that lines up Miquon pages with Singapore pages. That system just didn't seem to work for dd. She never wanted "more of the same". She likes variety.