Wow, she is a keeper.
The MP9 is a much different buggy, the MP777 WC is more of a tank, it weighs more, and can be driven much harder. The MP9 is lighter and more nimble, it has to be driven a bit more smooth, but it pays off because it is faster than the MP777, It handles better in just about every category, just it cannot be pushed quite as hard. But the only way for you to really know is to get it built and go put some fuel through it.
Although the design is similar to the MP777 it is actually much different, even though the diffs look similar they are much different, everything else is like that, similar looks, but in reality it is much different.
I currently have 5f 5c 2r in my buggy. Be sure to try the lime green springs up front, everyone I know runs them, they are a big improvement with our setups.
Good luck with the buggy, I love mine.