I agree with what ColinsMum wrote. I'd tend to stick to a syllabus ordering, especially for a well-respected program like Singapore Math.
As parents we might feel like the aim is to help our kids maximize their advancement in all areas, because we realize that asynchronous development implies that a child will be ready to do some things well in advance of their normal age-relative development in other areas. But you want your kid to have a good foundation in all important areas and sub-areas, too-- and I think that's easily as important.
Also, I don't think your child's ability to do, say, coordinate graphs work will be negatively impacted by putting more focus in the short term on areas where your child is
relatively weak, in math sub-topics that may be prerequisites for other sub-topics. I think that a lot of math is about the ability to think abstractly and manipulate symbols. While it might seem like focusing more on multiplication and division and fractions, for instance, would delay important abstract development, I don't think it's really the case, especially since you will probably find your child will pick up just about anything very quickly, and you'll be back to coordinate graphing and beyond before you know it.
IIRC Terence Tao's father, of all people, has said publicly that he didn't think it was as important to race ahead with new math concepts, as it was to build a strong, broad foundation in math. His son turned out okay.
Math geniuses throughout history have developed in times and with resources that were primitive compared to ours today. So I wouldn't sweat it too much, no matter what your approach turns out to be.
One thing you can do easily, as a parent, is called
"curriculum compacting", which includes testing out: you assess your child to see if she's okay to skip a lesson. You will just have to develop with her your ability to do this well. Present it as a valuable option for her-- it gets her out of boring work and you get to do more exciting stuff.
I wouldn't hesitate to add more grade-forward stuff as enrichment, but you will have to keep track of what you've covered, which will lose one of the big benefits of a curriculum. I see it more as an exercise in two things: 1) keeping enough "math stuff" in the pipeline so my child is growing, and 2) not forcing him to do boring work, which also increases the speed at which he can advance. I don't care much any more about the specific order, as long as he's learning well, and will go with a curriculum ordering that seems to make sense.
There is plenty of fun, challenging math work you can use to spice up the curriculum, and might also allow giving early assessments of whether your child can handle a certain grade-forward topic out of order.
I have really liked some workbooks recently that I bought for my son: the FlashKids "Math for the Gifted Student" and the mini-workbook "Problem Solving" series are both fun and interesting for my son. The big ones are around $10 US, the small ones (with still a lot of pages, just in a smaller format) around $4 US. What I did was rip or cut them out of the book and feed them through my printer/scanner, saving them as PDFs, so I can feed them to him out of order, he can look at them on the computer if he prefers, etc. Those workbooks are nice because they're quite inviting visually, no two are alike, and they work on a wide range of problem-solving skills which are important for math.
You might also decide to devote some time each week just to problem-solving or critical thinking skills. That's what I've done, and my grouping of material is a bit hodge-podge at the moment because I took material from such a wide range of sources. It includes a lot of material that is visual-spatial in nature, and hence more "mathy", together with more verbal stuff like analogies.
If you want to explore critical thinking, I recommend checking out the Critical Thinking website (although I'm not hawking their wares and am suggesting this just as a starting point), and Amazon for logic books for kids (although I'm not shilling for them and suggest their website just for its great search engine). Mindware.com is another okay place to start poking around. Critical Thinking offers a bunch of now-classic stuff like the "Building Thinking Skills" series, "mind benders", etc.
