Your lather will generally be about the same. Most brushes will create good lather, some however load product faster or mix is up more efficiently, though the final product should be very similar. That said I have a couple kabuki brushes with very very fine bristles that tend to mix lather that is finer and more gel like than a typical shaving brush. Though its not a black and white difference by any means.
Buying a high end shaving brush is more about face feel and visual appeal, than lather creation. I have plenty, and enjoy the variety of shaving experiences they provide me.