I am using Artlantis 6.5, and have been using Artlantis since version 4.
The multiple node rendering feature is quite nice, and seems to work well. I've only tried it with two computers, but it still significantly speeds up the process (which wasn't terribly slow to begin with).
The more significant difference you will experience with an upgrade is that in Version 6 Artlantis went to a physically correct rendering engine. Lots of good stuff here as well, but you will note some features have been dropped. Two that come to mind are the 3d channel for shaders, and soft shadows. I suspect that the change in engine forced this, and I hope that Abvent is working on bringing back these features, but there has been no official word.
The other change with Artlantis 6 was a slow down in the preview window, and I think some slow down in rendering. The improvements in 6.5 were meant to correct this, and even improve speed.
From my perspective, I am happy with 6.5, though I am hoping to see some lost features return soon.