Noflynomore- I am not sure What canaries flights that you have done which is longer than a LCA or PFO even with good weather it's around 4:10min going East and 4:25 coming West. Where most of my recent ACE,FUE and TFS have been less than 4hours.
I am not sure about all other crew but I always find LCA & PFO flights more challenging and tiring than Canary Islands flights. I think this is due to the amount of different countries and airspace your travel through with not so good English spoken by ATC and at night have lots of the heavy traffic heading East to Arabia and Asia