Condition implementation Problem

Just take this example :

 void Start ()
     {
         StartCoroutine("TriggerCubeAnimation");
     }


  IEnumerator TriggerCubeAnimation()
     {
         foreach (var o in cubes)
         {
           while (o.transform.position.y<fMaxLimit)
             {
                 o.transform.Translate(v3speed.x * Time.deltaTime, v3speed.y * Time.deltaTime , v3speed.z * Time.deltaTime);
                 Debug.Log(v3speed.x*Time.deltaTime + "  " + v3speed.y*Time.deltaTime + "  " + v3speed.z*Time.deltaTime);
                 yield return null;
             }
         }
        yield return new WaitForSeconds(1.0f); 
     }

I have Four Cubes in Row what i want is when my first cube start animation and when it reached at position 3.0f at Y-axix then the other cube start its animation all four cubes reached at 3.0Y in a row . like first then second then third and then fourth. and it does. But problem start when i want to make it faster if i make v3speed.y a big value it over reached the while condition and give some thing weired values.

for example : if fMaxLimit is 3.0f. then if i make v3speed.y = 20.0f the v3speed.y increses 20 per/sec and