Just a point of order on that: The G4-based Macs with DDR shouldn't be expected to run any faster than a unit with SDR at the same bus speed. Apple switched to a system controller that supported DDR for the late-model G4s because SDRAM was becoming obsolete, but no "G4" (IE, 74xx-family) CPU has a DDR-capable frontside bus.
If a 1Ghz DDR iMac G4 does indeed benchmark slower than an a 1Ghz eMac it's probably because of thermal constraints or, I dunno, bad karma.