I'm pretty sure I eliminated gamma variations. I tried both sorts of monitor attached to both Macs and PCs. The differences were consistent across the board. I didn't have good control of the ambient lighting, but again, the differences were consistent.

The Dells are good monitors, and I love the ones we have here for the task they were bought for (they are part of the design suite for a lithography system) but they don't make me want to part with my own money for my personal photographic use.