I would suggest testing both scenarios, and see which works best in your environment.
Hyperthreading will divide each processor/core into two virtual processors, which will double the number of "processors" available to programs. However, the performance of each virtual processor would be less than the physical processor. There is a tradeoff between the number of tasks that can be performed and the speed at which each task can be performed.
The following blog posting talks about some additional multi-threaded actions (beyond rendering):
http://revitoped.blogspot.com/2009/08/multi-coreprocessors-tech-note.html
Note: The multi-threaded commands noted are enabled by default in the current version of Revit (no need to manually enable as described in the link above).
While looking into this, I also found this interesting article that describes why scaling performance with multiple cores is not a straightforward task when dealing with non-discreet tasks:
http://redbolts.com/blog/post/2010/02/01/multi-core-scaling-of-the-Revit-Database.aspx
Lance Coffey
Technical Support Specialist