So far, out of experience, i can tell you that selenicereus and hylocereus grow fast, saguaro slow, ferocactus and stenocereus medium. Who can tell me out of experience(and preferably pictures) for the following cacti
- peniocereus gregii
- echinocereus willcoxia subgenus
- frailea
- gymnocalycium
- pachycereus pecten aboriginum(priority)
- pahycereys(lophocereus) schottii(priority)
- ariocarpus(maybe)
-thelocactus
- rebutia
-parodia
-eriosyce
-lobivia

I can't help, but I will be curious to hear what others have to say. - Interesting topic!

So much depends on the quality of the seed, not just germination but also the first few weeks of growth because viability is not an on/off switch--rather, it's a dial switch.

What I mean is that if you have fresh seeds from last year of any of these species, you're more likely to get higher germination and quicker growth than if your seeds are 5 years old. If your seeds are 20 years old, then you'll see even more drastic differences.

This is complicated when comparing growth rates across species because seed viability and longevity (which are not necessarily the same thing) vary across species, too.