Well, you could simply use you low poly mesh and smooth it to use it as an high poly mesh. This way you can bake an accurate normal map without the need to paint it.
You could also get the quad chamfer modifier plugin (Worth the cost) and use it to chamfer on smoothing group boundaries or within edge angle threshholds automatically to get a perfect smooth.
You can also use the custom vertex normals with a single segment chamfer to get perfect smoothing without a normal map and only a few extra polygons in controllable places.
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You could quadrify the low poly mesh with a modifier and throw a turbosmooth on it and then bake.
You can also use the custom vertex normals with a single segment chamfer to get perfect smoothing without a normal map and only a few extra polygons in controllable places.