Mostly I remember about where I am on the cassette and go
by the torque and cadence to determine shift points. CW:
I spend 85% of my time in the 42t middle and 0.5% in the
30T small, so I never get lost up there, but no big deal to
glance down. FWIW Shimano has an inline indicater for
about $10 that moves a little colored bead back and forth
in a clear window about 4-6" from the brifter and visually
indicates which gear you are in.