You've done well to troubleshoot your slow performance, by running DPC Latency Checker. Now you need to determine which drivers are causing the latency. Follow the guide on
http://www.thesycon.de/deu/latency_check.shtml.
If you have an Atheros WiFi card, the Atheros driver would be a good place to start...
Confirm you have at least 25% free space on your OS drive, then defragment it.
The Windows Registry gets bloated as you install and uninstall to it. You could give CCleaner a shot at cleaning up registry clutter.
But sometimes, a clean Windows 7 install with recent device drivers is the best way to inject new life into an old system. See
http://www.overclock.net/t/1156654/seans-windows-7-install-optimization-guide-for-ssds-hdds for a detailed guide on how to accomplish this...
I see you mentioned you just did an ASUS Factory Restore, so your Registry should be somewhat clean with OS drive not fragmented. Perhaps it's best to focus on resolving your DPC Latency issue...
G74SX-A1 - stock hardware - BIOS 202 - 2nd Monitor VISIO VF551XVT