NO NO NO NO NO NO.
V4 Models can be read, manipulated, and used in V5 without migrating them!
V4 3-D Models can be used in V5 CATProducts.
V4 3-D Models can be used in V5 CATDrawings.
V4 Drawings can be viewed in V5, although you may not like the way they look.
The only reason to migrate a V4 model to V5 is if you need to change something inside of it.
That being said, you will not be able to manipulate the parts inside of the model individually. So unless you modelled your V4 stuff mono-detail (i.e. one part per model), you may need to convert the parts to V5 in order to work with them.
The Batch utility works pretty good. If you have a V4 Model with multiple solids, sets, and details, it will automatically migrate that to a CATProduct with multiple CATParts. If there is a drawing, it will also migrate that. If your drawing used AUXVIEW2, it will automatically link the new CATDrawing to the new CATProduct. If you used transparent views, they will be migrated to Isolated Views in your CATDrawing with no link to the 3-D.