Melessa,dd4.5 loves math and is very mathy. She is not a fluent reader and does not enjoy reading. So kind of opposite but I have tried several math books with her including ixl, singapore math, and brainquest. he was finding 2nd grade math too easy and boring on all the three and I did not think she was ready for 3rd grade. So instead I got her this book.
http://www.amazon.com/Math-Gifted-Student-Challenging-Activities/dp/1411434331
Both of us love it. There is very little repetition and you actually have to think through the problems. I started her on first grade but planning to get the second grade soon. Barnes and Nobles has them, if you want to check them out at a store.
On another point in your post, DD can do multiplication and division even though she hasn't memorized any facts. She just uses various self-invented shortcuts. So I don't think you have to master the facts before moving on to advanced concepts with these kids. Once you give them a problem, they will use the tools they have or be motivated to learn the tools they need. I don't think learning the facts as an end goal would appeal to our kids. HTH