I personally believe that Aros68k will have lots of great features and enhancements in the future compared to 3.9, but unfortunately, it seems, it will never be as fast as the AmigaOS 3.x line, due to lack of adequate optimisations. And then, we all know how vital is to get the best performance, on a low end microprocessor system such as the Amiga.
Despite the improved code readability and maintenance Aros68k might provide, there is little a bloated C compiler can do better on Amiga, than the old tighly compiled assembler code, or even in the worst case scenario, the specificly designed Amiga 68k C compiler that has real optimisations built-in.
But then it is just my opinion...