I also created a document for the comparison between these two & your blogs helped me a lot. Thanks for sharing. I was wondering that why tableau is taking more time then powerpivot at the time of taking data for the first time, after that Tableau creates cache & executes faster then Power Pivot. Is there any best practice to overcome the time taken by Tableau?
The actual extract time between the two tools was pretty similar. However, for some reason, the compression and sorting done by Tableau after the extract was what took the rest of the time. Perhaps that's the reason why Tableau's data source was so much smaller than Power Pivot's. Alas, that is all theoretical at this point.
As far as the best practice goes, the only advice I can give is to say that the faster your source is, the faster the extract process will be. You can consider indexing your tables if they are in a database, or moving them to a faster server. There may be some people on the forums who can give advice on how to shape your data beforehand in order to cut down on the compression time.
Hope this helps,