Redlining is definitely there in MGE. Please have a look at the "MapGuide Viewer API Reference" - which is available in the MapGuide OpenSource or is there in the installation of MGE.
As we are also looking to move to MG6.5 from MGE, our concerns are much more compared to the functionality, which is fairly comparable between both. Performance, stability and scalability for large number of layers is something more in our mind, right now, esp. with live data served from Oracle.
-Praveen