I have an i7-2500k, 8GB RAM, a pair of Asus VH242H displays, an i1 Display Pro calibrator, and a Wacom tablet. It is fine for looking at photos but editing a 25MB .dng with lots of brushstrokes in LR4.1 can run it into the ground.
A faster processor and 12 or 16GB of RAM would be a better idea, as would one good monitor; The panels I have are remarkably inconsistent for brightness and color temperature.
The calibrator and the tablet are swell once you figure them out, applying adjustment brushes is much easier with the tablet.
The only other thing I'd change on this setup would be a faster drive array. I have for storing photos a RAID5 array of older mechanical drives on a proper 3Ware card but a bundle of SSDs would sure give it a kick in the pants. Win7 runs on its own Velociraptor, which is enough.