Indexing Speed

There are a number of things that may affect the speed of your indexing:

Leaving the window open while reindexing causes a slight degradation in Windows' performance. This is due to the overhead in Windows screen management. To run the update as fast as possible, minimize the window to an icon.
Using other Windows applications while reindexing will increase the time to complete the reindex, and you may experience some slowness in the use of the other programs.
Review which options you have selected. Things like date recognition, number recognition and entity detection all come at a cost.
The time required for the reindex will vary, depending on the number of changes that have occurred since the last update and the size of the index.
The use of Static Folders can reduce the time taken by updates dramatically.
Virus scanners can impact the speed of index building, it can be impacted in two ways:

Reading the documents - Perceptive Search must load the content of each document for indexing. Some virus scanners will scan each document as Perceptive Search requests it, slowing down the index run.
Creating the index files - depending on the amount of content you are indexing, the index files can become large. The building of these files can slow down as virus scanners scan each file.