64-bit Toys for Athlon-64?

gbulmash asks: "I'm looking to see just how much performance I can squeeze out of a new Athlon-64 system. This isn't for benchmarking, but more like you got a new car and you're looking for a long, straight road where you can push the needles into the red before letting off the gas (and then maybe a twisty mountain road to test cornering). Can the all-knowing Slashdot readers recommend some AMD-64 enabled/optimized distros and packages that will let us new proud papas of AMD-64 systems fully open up the throttle on these bad girls and see what they're made of?"