This would depend on the application.
Multi-threads by typical deffinition share memory in the same virtual address spacewhereas multi processes have different independent virtual address spaces.
If the application can be divided into processies that do not require rapid consolidation of results data then either system may be equally fast. The less the frequency of consolidation of results data might favor muilti processes as they can be run on completely seperate systems (i.e. no sharing of memory bandwidth).
However, if there is a high degree of rapid consolidation of results data then multi threads with shared memory would perform better.