120Hz mode on your TV is not the same thing as in an EVF. An original OM-D is also a whole different animal to any camera released in the past couple of years. Even going from my X-E2 to the X-Pro2 there was an obvious and clear difference. With my X-Pro2 however, I can't detect any difference in lag between the EVF or the OVF, both work great for sports (in fact, I prefer to use the EVF for it because I can see exactly where the focus is and what the meter is doing to the exposure).
Am well aware that 120Hz TV is not the same as 120Hz EVF, but I merely used the parallel to represent my own eye's inability to detect 60Hz vs. 120Hz, not to represent myself as someone with super keen sensitivity to the issue. I evaluated the EVF on Olympus within the past few years (I know, a 'lifetime' in terms of camera techology changes), to get a feel for EVF; more bothersome for me than viewfinder lag was the 'shimmer' I could see clearly in the store lighting.
The A9 is certainly a spectacular camera, one I wish I could afford to buy, to get me in a compact lighter kit more akin to the Olympus OM system I have had for 40 years, that was a joy to travel with. But even DPReview mentions the characteristic of lag in the A9, albeit tremendously reduced from prior generations of EVF
"The Sony Alpha 9 is the company's first camera aimed at professional wedding, action and sports photographers. It's a 24MP, full-frame mirrorless camera that can shoot at 20 frames per second with full autofocus. And, just as importantly, with very low viewfinder lag and absolutely no blackout during continuous shooting."
The YouTube videos show how well the AF tracking works, following a pole vaulter running at top speed toward camera position and not ever missing focus.
I did just watch Tony Northrup's own evallation of the A9 (pre-launch) and he did mention that with 4 runners on a track the camera would move AF point from one runner to another, in an undesired manner...hopefully Sony modified the behavior before the A9 was released.
A June 2017 review of the A9 is on the web: https://biglensfastshutter.com …by-a-sports-photographer/
Evil view finder was underwhelming. Apparently this EVF does 120fps, but there is a noticeable lag when moving the camera vigorously. In sports where vigorous camera movement is a must, this is a deal breaker. "
Olympus themselves talk about the OM-D EM1-II:
"Olympus's press release contains the following statement:
"With high-speed operation that includes a maximum frame rate of 120 fps and a minimum six-millisecond display time lag during shooting, users will never lose track of fast-moving subjects."
With something moving 90mph, 6 ms equates to being 'behind' the object's actual position by 9.5". While that certainly will not affect most folks, it can be problematic for others in the right set of circumstances. Track a jet travelling a slow (for a jet) 300 mph, and .006 sec. means you are aiming behind the jet's actual position by 32". There are some compensatory features that help in that circumstance (continuous shooting so shutter lag not an issue, no viewfinder blackout) but focus speed drops from 20 fps to 10 fps during continuous focus tracking.
Fuji themselves say this:
"Existing cameras display the image after the whole frame has been read from the processor, but on the X-T1, the image starts to display before the processor has completed developing the whole image, which reduces lag time and means the sensor and display are synchronized. Display lag time has also been reduced by increasing the frame rate compared to the X-E2.
The improvements mean the X-T1's EVF has a world's shortest delay of just 0.005 second. You may perceive almost no delay on the view finder compared to the real image."
NOT bashing, merely understanding where the limitations of the product lies, so you can try to work around some of them (when I finally can afford to buy one).