In general, the execution threads on the two processors will run in parallel. Only when they are accessing shared resources will their execution be serialized. The net result is that the two processors, working together, cannot equal the performance of two separate processors - but they will significantly beat the performance of a single processor.
The next thing you need to look at is the performance of the individual processors. You are talking about a 2013 processor versus a 2016 processors. That's three years of improvements; smaller, faster transistors, microcode improvements, architecture improvements, etc. Likely more can be done per clock cycle than the previous. Add to this that the power utilization per clock will also be improved.
So, summarizing - and looking very far down my thumb at them - other things being equal, the dual-processor system from 2013 will likely perform on-par or perhaps slightly better than the single processor system from 2016. The 2016 system will do so using less power, however.