This episode already aired 2 months ago and got kinda overlooked here, so better late than never?
Basically, the short summary is:
Some eco terrorist detonates a nuclear bomb in Central City. When Team Flash arrives at the scene, she still manages to trigger the bomb. Basically, the entire team is standing just a few feet before the bomb and it is already going off. Barry then goes into 'Flashtime'.
What happens throughout the episode can only be described as absolutely insane. Barry not only runs around the city, trying to find numerous solutions by taking several people into 'Flashtime' and talking to them, he even goes to another Earth to get Jay Garick to help him.
After everything fails, and Barry is already exhausted as fuck, he finally decides to enter the Speedforce itself and destroy the bomb through some lightning trick.
All the while, the explosion has only expanded by a few feet.
I for one think this has put Barry at WELL beyond lightspeed.
Unfortunately, I can't find too many good clips on Youtube
https://www.youtube.com/watch?v=PGfgZGTZjFo
https://www.youtube.com/watch?v=3ulh5R1A55Y
https://www.youtube.com/watch?v=Y4XgQ8Hfq2o