Don't hurry. Experiment with DNN 5 on your laptop, but wait to move the production site up, that is my advice now. Most changes in DNN 5 are about making DNN truely multi-language. Your site is plain old en-US so those new features can only complicate things. Many production sites still run on 4.9.5. People say it's the fastest version around.

Versions of DNN 5 below DNN 5.5 showed some problems with performance. This was solved in 5.5.0 but the remedy caused other problems. DNN 5.5 and 5.6 are opening the way for multi-language content but will need at least another stabilization update.

If the maintenance I suggested improved performance, then consider ¹) making the jump. You may have to update to DNN 5.4.4 in two steps. Search through the forums for "upgrade path". In between the two steps, you may have to upgrade some extensions. Check those out too.

Also: the minimum requirements will change halfway. Check that your database is SQL 2005, SQL 2000 will no longer do (but SQL Express is okay and will do the job). And you will need .Net framework 3.5 SP1 installed on the server.

(1) I say 'consider making', not 'make'. Weight the advantages against the disadvantages.