Go the lowlier laptops, as standard CF cards used in boot devices aren't as fast as you'd think - in some cases, much slower than a standard HD, certainly in your G3 laptops. Also put it in a laptop with a decent amount of RAM, so you can disable virtual memory (ie. 1400c or 3400c).

Also consider that a cheap PCMCIA --> CF adapter does let you boot from it in the 5300/1400/3400 models.

JB