Hmm that's odd considering you have really decent specs. But it could be a couple of issues.
What settings are you running your games at? If it's on Ultra, try reducing it to High or Medium and enable performance monitoring or benchmark monitoring (available in some games under the graphics options tab) so you can monitor your fps drops, when they occur, under what settings and loads. You can adjust settings from there to best optimize performance.
Next, I would ask you if you know what kind of storage is your hard drive? Solid State or Mechanical? If it's mechanical what RPM is it? This would be the speed at which the hard disk spins inside the drive. The standard speeds I believe are 5200 to 7200 rpms. Obviously a 5200 RPM drive will bottleneck your data more than a SSD or a 72OO rpm Hybrid or HDD.
I would also recommend upgrading to 16 GB RAM. I use that for gaming on my custom rig, and I can get away with high settings on almost all current titles coupled with a much older Radeon 29 270 DD Edition card. Your RAM could also be an issue with regards to your lagging.
Also, try and see if you need to update your Crimson Radeon Software and your graphics card drivers.
Hope this helps. ~ Fayenwolf