We have used SCM and CM methods from the beginning, not exclusively, but strongly CM in our house. My oldest is in 7th and we have taken the CAT test every year since 3rd grade and they always do quite well. Do not stress the tests, they are so broad because scope and sequence for ALL curriculum is different the tests are made to be pretty broad.
As for math we have used MUS since the beginning and we really like it. My oldest and youngest do well with math, but take a bit more time to master, and my middle child who just gets math does great with it too. Each just goes at their own pace, some fast some a little slower and it has not been a problem. I always remind them we all have different giftings.
Edit – what I like about MUS is that they can truly go at their own pace. If they show mastery after 1 or 2 days, move onto the next one lesson, if they need more practice do all the worksheets. We also never finish a book in a year, there are a lot of lessons, but I like that because then we continue into summer 2 or 3 days a week to keep math fresh in mind. When they finish they start the next book. For example, my youngest took a little longer to finish Alpha his first year so he finished Alpha mid way through second year. Just last week he fnished Beta and started Gamma this week, he will likely finish Gamma next Christmas and we will just start the next book at that point. I like that they are not grade level specific, we just keep moving through at the students pace. Slowing down and speeding up as needed. I also love the DVD it has been fantastic with pre algebra and levels below. I understand math but explain it is not my strong suit, so MUS video helps me stay consistent in methods and tips to help my kids.