It should be setting it directly, actually. There is no 12 byte move instruction, so it also has to do three moves, plus you get the method call overhead as well as having to push the values to the stack and probably storing the framepointer (if Acknex does that. Who knows anyways?!).

However, it doesn't matter. Whatever you think, this isn't and never will be your performance bottleneck. Use a profiler, see where it is slow and optimize these parts. These micro-optimizations are useless and you should pick whatever style you prefer, not what might get retired 30 μops earlier in the processor.