I have what I was told was E.tersheckii. Its a moderate grower for me. But,I'm in the SF bay area of moderate summer temps.
It is a tough cacti-mine was dug up I discovered later,by plumbers fixing a line. I replanted,and its gone on looking none the worse for wear.
I do know,it's nowhere's near as fast as the tree Euphorbia's. It could be tortoise and hair...the cacti will keep going up as the tree Euphorbia's branch out.

hare. sheesh.

thanks, saw a 10 year old one today and it is about 8-10 feet tall with three "arms". Good to know.

Very commonly available in southern California. I have several and they are slightly faster than Saguaros... but incredibly slow compared to something like a Euphorbia ingens.. my E ingens has grown over 15' in 3 years... my Echinopsis have grown maybe 2' in 5 years- both are now 4' tall (and they were several dozen years old at that time... grown in pots, though, until I got them). Super large, old Echinopsis like those seen at Lotusland are over 100 years old... you are not going to end up with a huge cactus in less than 20-30 years even with this species.. .you want to grow a big, fast cactus, get Neoraimondia... mine is about 15' tall now and it was only 5' 5 years ago when I got it... MUCH faster than any Echinopsis. Even Pachycereus are way faster grows than Echinopsis.

Lizard Vet,

Thanks for the great info! My Echinopsis terscheckii is 3+ feet tall now. The one I saw was easily 8 feet or taller and I would be super happy with that height. i guess I just have to wait 10 years. i will look into Neoraimondia though