As for speed, I'm sure some very specialized applications can do better if they have constraints that allow for specific optimization, but as far as a general library goes I haven't seen better performance than GMP personally.
MPFQ exists for short finite field work, but it hasn't achieved the popularity of GNU MP.
this is what software such as CMake was created to solve. I guess the solution is to extend CMake to support Rust :)
That's the problem with having multiple build systems. The fact that there is so much heterogeneity in C/C++ land means I spend way too much time trying to build things. When things are standardized, I don't have to think much about builds. They just work.
If build systems were made to interoperate (e.g. by having a common spec, or by implementing the same behavior), then we could have competing build systems without the fragmentation.