The slopes do start at a common 0,~700 and are different off idle, and in the transition into deceleration, both places I'd expect lower rotational mass to show up in such a log. Beyond that I have to agree, the rate of change is too similar for analysis by eye on a web optimized graph.
The net idle to redline to... Approaching idle still gains time, so this will benefit people that like to rev their favourite tune, too!
All kidding aside, if you are chasing every last bit of potential rotational energy, this should help.
Sampling rate over the 12Hz offered by the OFT may be needed. (I think that's the right rate...)