How can I create an index which would optimize this query:

SELECT CONVERT(CHAR(4),YEAR(Hit.AddDate))+REPLACE(STR(MONTH(Hit.AddDate),2),' ','0')+
 REPLACE(STR(DAY(Hit.AddDate),2),' ','0') AS lcChampNumero,
 COUNT(*) AS Compte,MIN(Hit.AddDate) AS AddDate
 FROM Hit
 WHERE Hit.NoServer=3
 GROUP BY CONVERT(CHAR(4),YEAR(Hit.AddDate))+REPLACE(STR(MONTH(Hit.AddDate),2),' ','0')+
 REPLACE(STR(DAY(Hit.AddDate),2),' ','0')
 ORDER BY 1 DESC 

I added an index NoServerAddDate which includes the NoServer and AddDate fields. I see that this has changed the execution plan. It does show that it uses it. However, my query is not any faster.

Is there a way to make it faster?

This is one on a Hit table having about two million records and all I need is a repartition on a daily basis with the count. The result returns presently 28 records.