Presume you already have a .416 mould? I have not got into paper patching but found when using cast bullets in my .404 the plain based bullet from the mould I had made did not perform so well. Applying a shoulder to the base and crimping on a 44cal gas check really did make them perform. If you go down the way of getting a mould for either .416 or .404 I wouldn't go plain base.
In saying that, it is easy enough to convert to gas checks if the plain base does not perform. I also like to crimp my cast loads if hunting with them and as Daryl points out, crimps and paper patching won't go well together.