eigs multithreaded scaling and max number of threads

Hi all, I was wondering if anyone had experience with using eigs in a multicore system for a relatively large problem (matrix rank ~100.000), does the performance scale linearly with number of threads? Or does it start saturating (probably depending on the size of the problem)? And finally, is there a limit of max number of threads for internally multithreaded functions (like eigs) in MATLAB? Cem