It seems to me that you have pretty well listed the pros and cons. Another small con for a 4 servo setup is two more servos that might fail... Another small con for the 2 servo setup is the interconnect. It has to be very stiff and vibration resistant...

I think I would go with 4 servos since you can use lesser torque servos. I also like using short control linkages which the interconnect is not. The hassle of running the leads and connectors up the center cabane doesn't seem like a big deal to me... I have a 2 servo GB Ultimate and fitting the interconnects is a pain and you always run the risk of leaving them at home since they are not permanently attached to the airframe. Ask me how I know about leaving items like these and hatches at home...