no idea who plays middle+ring but i can guarantee you that mania players have to gain speed and stamina in those fingers in order to play well on 7K maps.
to be completely honest with you, i wouldn't recommend playing osu!standard with middle + ring. try putting your hand flat on a table and lifting only your middle finger. then try it with your ring finger. you're going to feel like a disabled person trying to lift your ring finger as high as you can lift your middle. this is because of the tendon connecting your middle and ring finger - by lifting your ring finger, your middle finger wants to move with it as well.
unless the tendon connecting your ring and middle fingers is non-existent i strongly recommend you play with index + middle , index + ring, etc. because they are all much more independent than the ring finger and you will have much more control over your fingers.