I haven't hunted them extensivly but I have done a little solo-ing here. With harmony at lvl 54 I was able to find a few genoids that could be pulled a safe distance from the other surrounding genoids to kite. It's a tight squeeze for the single druid, would of worked much better with a group. So, as long as you have a druid/ranger and your group goes in invis you should be able to find a spot and start pulling till you hit the end of a tunnel. BTW be very careful of agro'ing genoids through walls as there are a lot of branches in the caves. Oh, and if I'm not mistaken genoids have about 10k HP. I wouldn't suggest any melee try to solo them. (made me oom with every pull)
Single pullable at 58, and Sk's can kite them easy by pulling them outside , just make sure you have lotsa mana in reserve.. look at my post under the regualr Geo's =)
me (52 monk) and a 51 cleric tried to take one out we got him to 25% after i used mend stone stance and he was oom, i was wielding a IFS 38/40 2hb and have a fbss, he had obviuosly speed himself and he also dispelled my hp buff right off the bat, so load a junk buff first, my buddy ended up gateing and I FD very tough.
I did over 3.6k damage to one of these things and only got it to about 60% total Hits. Lure of Ice works well against them (no resists at all) but Draught of Fire is frequently fully or partially resisted. Bring friends :)
If you are looking for harder quest gems to get, killing these are your best bet. I have hunted them for a long time and they seem to drop almost every crushed gem there is. The drop rate i would say on these, is about 50percent of the time, they drop a quest gem.