Photoshop :: CS5 Interface Gets Really Slow When Image Opened?

Photoshop gets really slow when any image, regardless of size is open. When there are no images open it runs smoothly. The interface gets really laggy, filter usage, tool selection or any other usage is really sluggish, but only with an image open, even if it's a single pixel.
 
I've tried different performance settings - changing where the scatch drive is, how much memory to allocate, what the cache levels are set at, enabling/disabling openGL, etc. It makes no difference if it's after a fresh reboot or if it's been on for days. No software has changed since the upgrade. Memory test don't show any issues and no other application has this problem - Illustrator, After Effects, Maya, Mudbox, etc. are all fine.
 
My system specs
 
Windows 7 x64 Enterprise - Service pack 1 installed
Dual Xeon quadcore E5620 @ 2.4GHx (sixteen threads w/hyperthreading)
96 GB Ram - DDR3 - 1333 MHz / PC3-10600 - registered - ECC
Nvidia Quadro FX 3800 - with latest stable performance drivers v 295.73 (tried changing these, no affect)
Western Digital VelociRaptor  150GB 10000 RPM 16MB Cache SATA 3.0Gb/s OS Drive
X3  Seagate Constellation 2TB 7200 RPM SAS 6Gb/s setup in a RAID 5 config
 
I'd think it would be a memory issue if all apps had similar problems, or if PS had issues when just being open. It's odd that it happens only when an image is open.