The only negative impact is whether you are skilled and geared enough to handle the heat. Its pretty random. Supposedly higher rank missions means stronger opponents and such but it makes no difference, stacking 20 low ranked missions still spawn Elite Anacondas and FDLs while stacking 20 high ranked missions, sometimes i didn't even bump into a single enemy.
Personally, i just stack as much high paying, high ranked missions as i can. So long as you have a good ship and some skills, you'll make it through.