Arguably the only gear I've tried to memorize speeds at is 6th -- Cuts down on the number of attempts at finding that elusive 7th gear when commuting...lol
I catch myself searching for a 6th gear on my VTX every now and then when at highway speeds. Always seems like the revs are so high.
One of the smarter things HD did on many of their bikes was opt for 6 speed boxes - makes way better use of the inherent torque in a V-Twin in the end.