The PowerPC 7447 "Apollo 7" is slightly improved from the 7450/55, it has a 512 KB on-chip L2 cache and was manufactured in a 130 nm process with SOI, hence drawing less power.
The only companies that offer the 7457 in the form of upgrades for the Power Mac G4, iMac G4, and Power Mac G4 Cube are Giga Designs, Sonnet Technology, Daystar Technology (they use the 7457 only for iMac G4 upgrades) and PowerLogix.