One of the three areas where Autodesk has made improvements in the 2014 release of Inventor is Customer Productivity, and more specifically, in Large Assembly Performance. Historically, Inventor has not been able to take full advantage of the graphics processing unit and has had to rely on View Representations and Levels of Detail options to curtail extended load times.
In this latest release Autodesk has developed an Express Mode for large assemblies. When Express Mode is enabled through the Application Options, users can experience a 5x-10x performance boost when it comes to opening these large assembly files. I recently had the opportunity to prove this enhancement in the real world, as I was invited to show a client the improved load times they could realize by upgrading their Inventor to the 2014 release. I opened their assembly file at more than 10x faster than they had previously been able. The assembly file opened in under 3 minutes, where it would normally take 35 minutes using a previous release. Everyone in the room instantly realized that the Large Assembly Performance was no joke, but instead, a true boost in productivity.
To enable Express Mode, go to the Tools Tab > Options Panel > Application Options, click the Assembly Tab, click Enable Express Mode.

Since some commands are disabled under Express Mode, setting the file threshold to a reasonable number will allow you to open smaller assemblies using Load Full mode, leaving all commands available for use. You can also UN-check Express Mode using the Options button when opening a large assembly.
Remember: Not all commands are available in Express Mode. If a required command is not available, then select Load Full.