My pump got weak and died over a period of several weeks. It would hardly run on B100. Adding petro diesel to a level of B20 or so would clear up the problem. The pump eventually died and took the #1 injector with it. Fortunately it was under the 100K warranty.
You are correct that it is slightly higher in viscosity. On the lower end of the viscosity scale however a slight change in viscosity can be double or triple that of petro diesel. Drop the temperature a few degrees and it increases exponentially.
I don't know how sensitive these pumps are to higher viscosity. That is why I now limit my Bio level to 50% when I wxpect temperatures below 50°F. Only time will tell if this is necessary.