SGP has a really helpful Framing and Mosaic Wizard that makes building mosaics up to 50 panels quite easy UNLESS you are going for a really wide field. Anything more than about 15-20°FOV can take forever to load.
For either more than 50 panels or for 20°+ I have found that TheSkyX is the best, especially after I came up with a way of importing TSX panel data into SGP for image capture.
For instance, when I was creating
this Milky Way mosaic with an 85mm lens and Nikon D7200, SGP couldn’t handle the wideness of the FOV but it took a minute to frame and create it in TSX.