As of February 12th, the glitch that resets the odometer has been fixed. I can confirm this myself. As mentioned already, this is best attempted on the Little Eagle Speedway.
This achievement roughly takes approximately 25hrs (200 miles an hour.)
I did this achievement entirely in the 2009 Mercedes SL65 AMG (Circuit - level 1289) across 3 days. The car would achieve 255mph normally and 270mph whilst drafting.
Having a partner to do parts of this with will make the process slightly quicker as you're able to draft them back and forth thus achieving a greater top speed along the straights.
Another tip, if you're coming across some other playing trying to crash into you head on, then just before you think you're about to crash, simply press the back button to go to the map, your vehicle will become invisible (ghost status) and so the opponent will drive right through you, immediately return to the game and you will still be on track with the same speed as when you paused.