Sun Firms Up Its Sparc Chip Plans
delirium of disorder writes "Despite their recent focus on Opteron-based servers, Sun has not given up on SPARC. Niagara , the latest development in the SPARC line, will have 8 cores and according to this article will consume about 56 watts and have performance comparable to a four-way SMP Xeon system. New Xeons will consume hundreds of watts per processor."
While the registers visible are limited to 16 in 64bit mode there are way more registers available to the cpu via register renaming. It does add a bunch of transistors but its no longer killing the performance. More AMD64 Info