What is the optimal response time for file growth We normally set our file growth in percent (10%,20%) or fixed size (10 MB, 20 MB etc). If the disk response time is too high for the requested size to grow, then users will be affected and have to wait until the file growth completed. We can see the response time in micro seconds at default trace file column named as 'Duration'. 

My question is, what is the optimal response time for every growth in milliseconds?
First of all you want to make sure that your database is sized appropriately up front.  Usually I like to plan for 6 months to a years worth of growth.  That being said your data file(s) should be the only ones growing on a regular/irregular basis.  Your log file once it hits a certain point should not grow much if at all, assuming you are taking regular backups.  Given that, you can use a server setting called Instant file initialization that will make your database growth very very quick, regardless of how much space you are adding.

Here is a link you can read to start you on it.  http://msdn.microsoft.com/en-us/library/ms175935(v=sql.105).aspx

If you have this turned on then you can afford to set your auto growth to larger sizes so that you don't have to grow as often.