For rendering, just use Motors (Motor1D/Motor6D) and not Welds. Updating C0/C1 for Welds is still expensive and will probably stay that way.
I don’t think there are any real caveats for replication. If we expose the CFrame of the motor the replication may get more efficient but I’m not entirely sure about that - we optimize angle replication for motors only in the physics channel, and property updates don’t go through that.
Now C0/C1 updates for motors just update the internal cframe data pretty much, and then rendering treats the parts as independently moving - so having a motor that connects two moving parts is same cost for rendering as two independently cframed parts (probably this is more efficient than just cframing parts for other parts of the system).