MacRumors.com

Several news outlets have reported on the newly released Beta compilers from IBM.

XL C and XL C++ for Mac OS X (download here) are PowerPC 970 optimized versions of IBM's compilers which have been show to improve Power4's SPEC performance (PDF) significantly.

Some early benchmarks (Ars Thread) demonstrate significant performance boosts -- up to +210% in Scalar performance in one particular PowerMac G5 Fortran application -- with more modest improvements in other measures. The code utilized in this benchmark appears to be the Jet3d codebase used in the early "NASA" G5 Benchmarks.