hmmm. I doubt that...
I tried to use your modified kernels (cubehash, blakekeccak,bmw) and I mostly see no difference.
there are some variability in the result but on a medium/long run it goes down to the same values I get with the standard kernels...
If the values go down over time it meens that your cards are trottling, because of heat or too low voltage. On my gtx 970 the miner is mining 500KHASH faster than yours.
Release 62 standard clocks:
(the 980ti is clocked at 1260 on the core)
well, the argument isn't really relevant, if throttling happens it happens in the same way for every kernels (slow or fast), so if a kernel is faster it will remain faster no matter of any throttling and here it isn't the case...
(test was done using default clock and tdp target of 100%)
If a kernel is faster it probably also draw more power, which in turn means more heat so higher chance of throttling.
If an enhancement to a kernel has the same performance/watt ratio as the original, the card may throttle and bring the same performance using the same power but a lower clock speed.
I'm talking general as I don't know if it's valid for this specific case.