What length of cobbles will you will riding?
Rather like LWB, I did the full amount as per PR race and would support his comments. As an aside, my audax bike has foam under the tape anyway, but only on the tops. Having done cyclo-cross prepared me for the sudden change when you go from tarmac to cobbles and although you are tempted to slow down, you must hit them at speed and keep going as best you can; don't slow down. Velcro on pump essential and if you have not got them already, buy some metal bottle cages that can be bent to really secure the water bottles. First section of cobbles was strewn with pumps and bottles! Careful with the amount of air in the tyres as there is a temptation to inflate too hard. If I did it gain, I would be using my CX bike with 32-35 tyres. Finally, get used to the term pave!