For more than a year now, the top end Macintosh product has been stuck at a now limited 500MhHz. Motorola and IBM have yet to produce faster G4is in quantity, and the Mac world awaits a sign that a faster chip is truly on the horizon. An interesting tidbit was discovered at the IBM web site by XLRBYourMac, indicating that IBM has 700MHz G3 chips ready to roll.
The recently announced low-power 750CX and 750CXe are said to be available at speeds up to 700MHz. No Macintosh product, however, has yet to been announced built on the new breed of G3. While the site touts 700MHz speeds, a chip not previously known to exist for the public, a quick look at the performance charts provided by IBM only list chips up to 550MHz, speeds we have known about for some time.
The IBM pages talks about the "Scalable PowerPC architecture" and indicates that chips at various speeds are available for different customer needs.