Mike, I shoot aluminums pretty much exclusively. Not that it matters though since the same principles apply that apply to tuning any arrow material. To answer your questin though, the first thing I would ask is whether your current arrow is dead on, a little weak, or a little stiff. If it's already just a tad to the weak side, (barely discernible when bare shafting) which is how I like to end up with my finished arrows, I would say 3/4" would leave me with less than adequate arrow flight. If your lucky enough to currently be a little over spined, you may come out just right. If your getting dead straight bare shaft flight, well...thats a judgement call that I think you'll have to make by analyzing the flight you end up with. If it were me in that case, I would probably try to procure a 2020 just to see how much more than that 3/4" I would need to get back to perfect tune. The 2020 may end up requiring more length than your happy with in that case in which case your back to the 2018. I hope my ramblings might be useful to you.