MySQL 5.1.x: Performance improvement in Enterprise edition Vs community edition My application is running on MySQL 5.1.58 community edition. 
I tried to search enterprise edition of MySQL 5.1.X but only MySQL 5.6.X version of enterprise edition is available.
Is it possible to download MySQL 5.1.x enterprise edition - trial version? I want to compare the performance testing with the community edition of MySQL 5.1.X
I don't think you can get a MySQL Enterprise edition for v5.1.X version.

You can see the diffrence in performance between Community and Enterprise version here:

http://www.mysql.com/products/enterprise/scalability.html

You can also download Enterprise product guide whitepaper to know more details.

In summary additional features in MySQL Enterprise version are MySQL Thread Pool, MySQL Enterprise audit and a Technical support for your server related issues.