If your desire is to improve performance, there are three areas to focus on.
1> SQL Server Express 64bit - if you have installed fresh recently, this is already in place. If you have been upgrading for a few years, you may be on the 32bit SQL Express. The next step beyond this is SQL Server Standard
2> More RAM on your server
3> More processing power on your AC server - this means newer, more expensive hardware
Storage is typically not the issue.
