Jeff,
That's great that you have a lab to test. I always advise my clients to have a test server environment to verify the upgrade before going live.
To answer your question, Microsoft has pretty much always been on the "2 version max rule". What this means, is to go to GP 2013 you would need to be on GP 10.0 or higher to upgrade to 2013.
So, you would go from 9.0 to 10.0 and then from 10.0 to 2013. You could also go from 9.0 to 2010 and then 2010 to 2013, but there were significant changes in 10.0 from 9.0, and to ensure that all those changes properly get upgraded in your DB, I recommend 9 to 10 and then 10 to 2013. However, since you don't have the latest service pack installed for GP 9, you need to install the newest service pack for 9 before upgrading to 2010.
If you have any issues, post-upgrade with your data, and certain things not working, then I recommend back tracking and seeing when it broke, i.e. was it from 9 to 10, or was it when i went from 10 to 2013. If it was 10 to 2013, then go from 10 to 2010 first and see what happens.
Here's a great post from Jonathan Fear on this same subject:
Dynamics GP 9.0/SQL 2000/Windows 2003 to Dynamics GP 2013/SQL 2012/Windows 2012
1. The first step depends on the version of GP 9 you are on. If you are on 9.00.0371 or later you can upgrade directly to GP 2010, however if you are not then you need to upgrade to 9.00.0371. Click HERE to go to the GP 9.0 Download Page to grab the required patch. If you are on a build later than 9.00.371 your upgrade paths may vary. Please visit the Upgrade Hot Topic page.
2. Once you are on 9.00.0371 or later you will want to move your databases to SQL 2012 on Windows 2012. Refer to KB 878449 for move steps.
3. Next you can upgrade directly to any build of GP 2010, I would recommend GP 2010 SP 3 (11.00.2044) as this will allow you to upgrade to any build of GP 2013. Click HERE to go to the GP 2010 Download Page to grab the required patch.
4. Finally you will be able to upgrade to any specific build of GP 2013.