This is true, but clang is new software under active development. The intention of the project is not to trade off speed for correctness but to eventually be c

This is true, but clang is new software under active development. The intention of the project is not to trade off speed for correctness but to eventually be correct and fast. According to the follow-up posts, the differences in rendering may largely be due to bugs in the floating point code generation. Once these are fixed, it is entirely possible that clang could generate the correct images at the higher speed. We won't know until then, however.