Definately give it a shot - you'll get at least ~ 30% better performance using the 1Ghz G4, see these benchmarks:

http://www.xlr8yourmac.com/g3CARDS/G3_1.1GHz_vs_G4_1GHz_review/index.html

It is a strange bug in that the Sonnet upgrade downclocks the bus speed to 66Mhz, I'm not a huge fan of their accelerators as you can't "tweak" them unlike pretty much any other brand. But I begrudgingly admit Sonnet upgrades are always reliable, well built and the company is still around at least

JB