There are lot of other factors that influence User Interface Rendering.
First and foremost thing, that comes to my mind is the network latency. Network Latency is the time taken for the result to reach the client from the webserver. Note that there can be additional overhead in the web server, that takes the data from the stored procedure and may involve other computations on the webserver side.
Use Network monitoring tools such as Fiddler/Http Analyzer to find the network latency time or the round trip time.
If you can use fiddler, this is how it would look. See the "Statistics" tab.
Hope this helps.