yes, there was a performance issue associated with this function in IPP 4.x which was fixed in IPP 5.1, so you may expect visible performance gain after migrating to IPP 5.x
BTW, there are other reasons to migrate on the latest IPP version. In IPP 5.3 we do support the latest Intel processor architecture, Core2 including the newest 45-nmfamily ofprocessors with SSE 4.1, many performance improvements across the libraries and some bug fixes.
Please be note, there were some limited changes in API between IPP 4.x and IPP 5.x. We do provide the full list of affected functions (you may fiind it on IPP Technical Resources page). Some redundant functions were removed.