I'd love to read your review and comparison. The first obvious comparison for me is the "smoothness" and "subtlety" of the venturi effect in the Atomic vs. the SP. As you know, the Venturi is automatically controlled in the Atomic second stage. It opens up to the fully open position at around 20 meters. I can sense that gradual change in the venturi effect.
I am definitely looking forward to comparing them. But, I'm not sure how soon I'll be able to do a thorough and proper comparison. As you imply, I need to go deeper than normal training depths to give them a good comparison. And, these days, I am generally only diving OC during training - so, not deep. But, I might take a special trip out to the lake where I can at least get to 27m (90') or so, just to get in with my doubles and see how they do.