Actualy it is not low.
you can write in options (only this:)
-benchmark 100
-benchmark 360
And see what is the difference.
Well Nvidia GPUs degrade in hashrate in ethash alghoritm !
I wrote to nvidia many emails about that problem but they do not give a F.

Previously 110watt was hashing 30-31MH/s
Now 135watt does not reach 28MH/s

So you can set higher wattage limit and beside there is no solution.
Most probably they do not want to make driver fix or their cards are bad compared to AMD which released dag fix patch for performance degradation for memory fragmentation problem.