The GPU is fine, but that build needs more RAM and possibly a better CPU. Would benefit significantly from an SSD; spend ~$100 on a 128GB SSD and watch your loading times drop.
My machine is always on. Subjectively, having 24GB of RAM made far more of a performance difference than my Plextor PX-256M3P, presumably because with 24GB of RAM pretty much everything of importance ends up being cached in RAM sooner or later.
yup, 8 Gigs of RAM should be mandatory. Also a i5 3720 has a excellent performance/price ratio.