My unpopular opinion is keep the R3, I would pick it over R5mkii for sports and I would keep the R8 for my walk around camera.
This is what I have been doing, and it worked well for me. However, I really did want a usable precapture for shooting kids at bat. It's not fun to shoot every pitch at 30fps, because I cannot know if they are going to swing and hit the ball. The R8's precapture is not well implemented and it is a hassle to use in reality. Also, there is rolling shutter effects on the bat and ball sometimes due to the slower shutter.
Thank you for commenting.