Hello Kevin,
I have just scanned a number of Sitting Helvetia covers. I'm most interested in different rates and how the various denominations were used. I'll start with two tonight.
Neuchatel 4 April 1864 to London, 5 April, via Pontarlier, France. The 60 centimes rate was in effect starting 15/8/1859, ending 30/9/1865.
Geneve 18 June 1864 to Turin, Italy 18 June. Triple weight letter rate in effect starting 1 July 1862 through UPU.