does merging tables always increases performance?
Without any knowledge about the workload of the database, is almost impossible to answer to a question like this. How often those “extra” data will be used? What are the most common queries? How frequent they are? and how much it is important the speed of the execution? 

The general advice is always the best one for me: make things as simple as possible, than optimize if you need to.

So my advice is: create a single table, look at the performances, and only if those performances are not adequate to your objectives, split the table.