DxOMark's review of the Sony α9 gives the camera an overall score of 92 outpacing the rival pro DSLRs from Canon (1DX II) and Nikon (D5) which both have overall 88s from the DxOMark testing regimen. In acknowledging Sony's technology advancements, the reviewers state, "Combine all that with its body-integrated 5-axis image stabilization system, effective up to 5 stops, and a maximum 204,800 ISO sensor sensitivity, the α9 shapes up as a performance powerhouse for professional action and low-light photographers."
And in their conclusion they write:
"The α9’s key specifications, including the 20fps burst shooting with full AF/AE tracking, no EVF blackout, near-complete autofocus frame coverage, and silent operation, are going to be seriously attractive to any and all professional action photographers.
"To help facilitate the super-fast performance, the α9 has taken a step back from the monster resolution of the α7R II, but its 24.4Mp chip should suffice for most, and overall its image quality is outstanding.
"The Sony α9’s sensor ranks as one of the best we’ve tested at base ISO, with consistently good scores for dynamic range and color depth, and exceptional results for noise. At those crucial mid to high ISO sensitivities for action photographers, image quality is also excellent and on par with flagship Nikon and Canon sports DSLRs."