I have tested some more. Release 74 is using more power and heat, so the card trottle and performance is lost.
My test was conducted in a closed case rig with a EVGA superclocked card (2x 6pins power)
but my dev card:
The gigabyte 970oc G1 comes with 1x8 pin and 1x6 pin and doesn't trottle and give bether performance in release 74 than 66.
SP_, all 5.2 maxwells do at least 1500MHz under load. In open case, limiting factor is TDP. Nothing to do with power pins.
-edit
Testing how far I can go with reference 970. You need to give this baby almost +300 to get there (1500). Around 10500 kH/s mining lyra2v2.
-edit2
Same settings with quark, hitting TDP and only hashing about 17200 kH/s. TDP mod is all you need if you want to get all out of these.