I takes about 30 seconds to plot a route that is 80+ Ly. And if you want to jump more than 100 Ly, then you have to chunk out your travels in segments of 100 Lys. What I generally do is find the furthest point that is 100 Ly in direction I want to go, plot route there, jump there and then plan another route to my original destination.
But I imagine I would loose my mind plotting 3000+ LY jump like this. It is no understatement when you say long distance travel is its own form of art right now in Elite. The nav computer needs to get boost and calculate at least 500 Ly. Our CPUs can handle it.