I generally haven't had a tach, and I go more by sound than by any gauge. Rear end ratio also dictates when you can shift. With my 88, I generally am about to cruise speed when I shift, but it had 3.08 rears. Most times, think of 5th like a lock up clutch, when you are to the speed you want, and have leveled off, go for 5th. Or the same for an auto, they typically do not shift to overdrive until you are light on the pedal.
Good to know. Thanks. I never thought of it this way. I learned from prior owner to start out in 2nd, get moving and then, fairly soon, to get into third, but I had no experience at all re when to from 4th to 5th.