-600' or -700' (2-2.3 miles) separation is when it gets interesting. -900' (3 miles) should always work unless there's buffoonery involved. Previous a/c has their act together, and works to make the first available turnoff and exits quickly, it works.

Had -600' separation 2 weeks ago. There's a 90 degree turnoff that the majority of guys make. Float, extra speed, long aimpoint, and the next taxiway is a long way down. Guys did a nice job, cleared when we were probably <100', and everyone was happy.