Is it kinder to the viscous coupling of my Panda Climbing to have equal tire pressures front and rear?

The answer is to use 'the correct' tyre pressures. Because the car is heavier at the front (the weight of the engine), the front pressure is a couple of PSI more, but the weight will 'squash' the tyre down and the rolling size be the same as the rears. (The pressures would have to be very 'off' to affect the 4x4 coupling - it's happy to cope with a few mm difference caused by tyre wear too)

What will harm the viscous coupling is a suspended tow after breaking down. I worked with a guy who bought an old Landrover, no vc of course, it was not happy in 4wd, he found out that the front and rear axel ratio's were different.