What makes you think quicksort is faster in C? I just tried a quick check of Julia's built-in sort! function vs. C's qsort function for 10^7 random int32 values, and Julia's was 2x faster.
Using a much simpler unoptimized quicksort implementation, the benchmark numbers are also pretty close to C (http://julialang.org/benchmarks/). This is not to say that things cannot be improved, especially for particular datatypes and applications (see also https://github.com/JuliaLang/julia/issues/939), just that Julia does not seem particularly bad here. Did you have a specific case where you observed a problem?
