Where did I go wrong?

We had a computer built for Premier Pro, but we are disappointed. We are new to Pro 5.5, so maybe we are expecting too much. Almost any video transition must be rendered. Everything seems slow compared to our old Velocity HD system. How would you rate the following system for running Premier Pro and After Effects?
16GB RAM
3.4 GHz Intel i7 Quadcore CPU w/Hyperthreading w/SuperMicro C7P67 motherboard
(1) 1TB 6Gbs SATA 7200RPM Seagate HD, Partitioned for C, Swap and Projects
(2) 1Tb 6Gbs SATA 7200RPM Seagate HDs, Striped as Video Drive
G-Force 570 1.25GB, dual-monitor VGA w/DVI
Windows-7 Professional; 64bit OS
BlackMagic Intensity Pro Capture Card

Thanks,
Bruce