SQL Server 2008 Partitioning Evaluation
What do you expect your real life volume of data to be? 

For 10 million rows, I wouldn't bother with partitioning. The overhead far outweighs the benefits: partitioning isn't a silver bullet to cure performance issues.

To answer, 

Point 1: on the first run, data needs loaded into memory ("buffer pool") and will stay cached until evicted based on memory pressure and usage. Personally, I'd test with the cache filled because you'd expect your app to require that data very often, especially if you think partitioning is the solution to some problem

For point 2, what queries do you expect to run in production? The queries should be representative of this production load. However they should test different realistic filter combinations with and without partition key at least.

Edit, some reading, after comments below:


http://www.brentozar.com/archive/2008/06/sql-server-partitioning-not-the-answer-to-everything/
http://www.mssqltips.com/sqlservertip/1914/sql-server-database-partitioning-myths-and-truths/ (point 7 especially)