I used to ride 606 on my Honda XR600 and was happy about them. I did not ride agresivelly - motocross like, but rather turist kind. Neverthelles I used to go any crazy complicated and steep lane imaginable and never found 606 to be insufficient regarding grip.
On the road I haven't found any troubles, but XR was not a fast bike ( max. 115 kph).

Now I ride XT660Z Tenere with Tourances and for me there is no comparision with 606 at all. Tourances are very good road tires with some marginal off road ability - just enough to allow comfortable ride on the good dry forest dirt roads. On the gravel however, one must be very cautious.
On the highway I found ride very good indeed, but for off roading I do not think even for the moment to go lanes I used to do regulary with 606.

When Tourances are going to be wored enough, I'am planning to switch on either 606, TKC80 or maybe MT21, whatever will be available. If possibile I will try to get 606 again.