I have Kingsrow at 1 minute/game (its doing about 4000-5000 Knodes/second). Results up to now are:
On my i7 940 ( 2.93 GHZ) Kingsrow runs on1 core at a speed of 3000 - 4000 Knodes/second , next to that Kingsrow does not use pondering and uses a 6p DB.
At least your "plies" seem to be more effective (and i recognize that ply is not very well defined as all programs use different extensions and pruning mechanisms) than the very selective ply I use, which create more depth , but at a cost.
The effectiveness could also be related to your evaluation.
I'm curious what higher depths reveal in your case.
If Kingsrow runs with more Knodes/second (as you use 2 cores) , the program most likely will be somewhat stronger (although with parallel search you can not translate kNodes/sec directly into depth anymore) than the Kingsrow I use as a base, as a consequence the asymptotic max ELO level in your test should be somewhat smaller. But as you still see more or less linear behavior it is to early to tell..
I will also do some tests at lower ply depth with all search enhancements switched off, and measure the effect...
Last but not least, what is the average game time for Dragon at ply 12?
Bert