The analysis in your link of this document is very flawed. They only consider tailpipe emissions from a gas vehicle. Without considering the GHG cost of an electric car in total vs cost to manufacture an equivalent gas vehicle in addition to the lifecycle GHG cost of extracting, refining and burning fuel, the time to payback is artificially inflated. An apples-to-apples analysis results in electrics having a much more favorable outcome (I have done this myself in the past).
Also, as more renewable electricity production comes online the numbers will continue to become more in favor of electrics.