These results of MacBench 4.0 might not be good guide to compare the original card and the G3 card, but I hope it could help you to imagine the difference between them. ("PowerBook" indicates original PowerBook2400c/180.

The G3 processor runs about three times faster than PowerPC603e/180, While the G3 card without backside cashe only performs half the speed of with backside cashe, it performs better than the original PowerPC603e/180.

Sorry, I did not have the result of floating point of PowerPC603e/180.

Video function performs twice better than the original. Backside cashe does not affect it.