My rule of thumb is just to go by feel. I wouldn't stop if the technique is getting hindered only because the weight is a high percentage. If you keep making the reps, then keep going up.
If you miss a max attempt but it's just a slight technical issue then you'll be okay to try it again, or even two more times if needed. If you miss a max attempt because it's too heavy then you may want to rethink attempting that weight again. For example, almost dropping the bar on your head in a maximum snatch attempt.