Abeka Arithmetic 4 vs. Abeka Arithmetic 5

We are an Abeka math family… it has worked for us for the past two years, so we plan to stick with what works. Here is my question… We are almost done with 4th grade math, and I bought the 5th grade level recently. In previewing it for next school year, it looks almost the same for an entire semester?! Up until halfway through the book, it looks like review from 4th grade. Does anyone else use it that can give me some insight? This is for my gifted student, and I think he will be bored to tears reviewing for an entire semester what we already mastered this year…