Neu motors and gearbox?

It been awhile since I last posted and was starting to get back into rc's and had a few questions. I plan on building a RC8T and was going togo with a neu 1515 1y motor again since I fell in love with my last one. I was on castles website and I see that they offer them with three different gearbox combos, So my question is......are they a nice thing to have or even necessary for a truggy? and would gearing be different?