don't remember ever being asked about speed unless we were testing...otherwise the tc gave speeds with words like "slow", "slower", "slowly", "easy", "faster", "move", "haul ass", "stop", "hold it", "backup" and some form of left or right with a clock position.
none the less, a small speed indicator in an out of the way spot wouldn't be a bad thing...
"M1C1" of Duxford Wing RAF, is a vet of Gulf War I and of Iraqi Freedom serving in all roles while in a M1A1 Abrams. He mentioned in terms of speed, the TC would typically call for "stop, quarter, half, 3/4, or full" (same for reverse), or a specified speedvalue (20mph). For directional, the clock position was typical as you mentioned.
Each TC was a bit different, he/she would cater to the skill level and experience of the crew.