We have a mix of Cisco 6500s and 4500s all running MST although the 4500 are running pre-standards MST. Looking at the link http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/configuration/guide/mst.html the maximim MST instances per region is 65 is this the case for standards and pre standards based MST on the above platforms also does the 4500/6500 have hardware/platform specific limitations on the number of MST instances.