It depends.

The G3 is heavily based on the 603 architecture, which in itself is inferior to the 604/e. But a couple of clever improvements did put the G3 far ahead of the 603, and in many cases it outperforms the 604/e at the same clock speed. Mainly because of the L2 cache and a redesign of the branch prediction unit that manage to keep its shorter instruction window full. 

BUT, if the software is coded to take full benefit of the dual 604 cpus, then its a different story.