According to the very knowledgable guy who built my PC, every program (Reason, Cubase etc) uses large amounts of ram. Once you begin adding vsts and Res then that's even more ram. By the time you've got all of this running you'll more than likely have gone past your 8Gb of ram and you'll be using hard drive space as virtual ram. Apparently this isn't good for it! This guy's company builds PCs specifically for audio use, nothing else.
Yes, your CPU probably should be maxed out here but I'd recommend getting that 16Gb ram kit which should easily deal with loads you're putting it under.
Won't cost that much either!