Agressive memory timings would be the result of chosing Turbo1 or Turbo2. You'll get higher performance/benchmarks, but your RAM has to be able to handle it. The delayed transaction setting is for compatibility, you generally don't need to have it enabled.
Edit: The two 256Mb sticks of Crucial DDR in my ANUS rig are rock solid at Turbo1, but not Turbo2. Your results may vary depending on your RAM.