It's way harder without the shift indicator. and some cars (corvette) have completely illegible dashes so you don't even know how fast you're going. But, yea I still drive with the HUD off quite a bit.
It's harder without the HUD although I've turned off suggested gear. Although I do play by ear, not having a DS3 makes the tactile feedback poor. And I usually overshoot it without a HUD. Still fun.