For some upcoming blogs, I wanted to elaborate on how DC organizes it's speed since it's a pretty unique way. 

See, in real life there are 2 sort of "barriers" to speed that we like to talk about. 

The first of these is the Sound Barrier, which is a point where if you go fast enough in an atmosphere you create a distortion in that atmosphere. The exact speed depends on what atmosphere you are in. Because this sonic boom destroys a lot of things trying to reach it, it was widely thought to be impossible to breach since it would destroy anything that tried it, at least in atmosphere since every planet and star is moving well beyond the speed of sound on earth.   

The second of these is the Light Barrier, which as far as we know is impossible to exceed or match for anything with mass. This speed is exactly c=299,972,458 meters per second. 

The way DC does this is they have a set of barriers, and their characters don't have any normal maximum speed, instead they have a speed barrier they can't break. Characters that are between the same two barriers will tend to be treated like they are around the same tier. Characters often have reactions 1 tier above their own speed tier, but characters that are 2 tiers below look completely frozen. 

Tier 5: Fodder Tier: Below Sound Barrier


Characters that are below the sound barrier are most normal humans as well as general fighter type people. There is not much to be said about these types. 

Tier 4: Low Tier: Between Sound Barrier and Light Barrier:


These characters can break the speed barrier for our planet, the sound barrier, but not the speed barrier for the universe, the light barrier.

Now there really is sort of two kinds of people in this tier and this is this the only case where that happens.

You've got the Lower Tier 4: which are the sort of "Peak Humans" and the "Street Levelers" who get to the high levels of speed, which are like Hypersonic or so. You've also got the Higher Tier 4, who are people that actually have superspeed as like an auxiliary power not a "real" super speed. "Enhanced" speed if you will. These are like lightning-timers and stuff. 

Note people on this tier will be treated as the same speed a lot of the time.

People on this tier have the ability to create a destructive sonic boom for a quick attack as well as blitz people. There is also the infamous "lightfingers" technique they can do where they can quickly defeat an enemy much faster then them by blitzing them before they realize there is a fight and so their adrenaline and reflexes get up. Batman has disarmed at least two green lanterns this way.    

Tier 3: Mid Tier: Between the Light Barrier and the Time Barrier


These characters can break the speed barrier of the universe, the speed of light, but can't break the time barrier, the speed barrier of the timeline. 

Most DC characters with prominent super speed are around this level of speed normally. 

This level of speed also the usage of vibrating to phase intangible and go invisible, as well as the ability to move near the speed of light for the famous Infinite Mass Punch using relativistic mass to create a super dense punch. How dense the IMP is depends how close the user can get to the speed of light without exceeding it (since your mass-energy actually decreases the higher above lightspeed you go). 

Tier 2: High Tier: Between the Time Barrier and the Dimensional Barrier


These characters can break the time barrier, the speed limit of the timeline, but not the Dimensional Barrier, the speed limit of the Multiverse. 

Most Super-Speed Characters pushing themselves reach this level and most Speedster characters (characters known for being really really fast in-verse) are here casually. 

At this level the characters gets as one might expect the ability to move through time at will. This allows them to do things like exist in multiple places at once or outrace instantaneous movement by appearing there in the past. It also allows for the infamous "time booms", creating disruptions in the timelines which can cause alterations in the entire multiverse though these are rarely precise in any capacity.

Tier 1: Super-High Tier: Between the Dimensional Barrier and The Speed Force Barrier


These characters can break the dimensional barrier, the speed limit of the multiverse, but not exceed the Speed Force Barrier, the speed limit of creation. 

There isn't actually many characters at this level and I postulate that it's because the dimensional barrier is really close to the Speed Force Barrier so if you break the former you likely break the later.

Beings at this level gain the ability to enter the bleed barrier and the multiversal orrey of worlds. One can theoretically vibrate into any world one wants though this requires precision. I think perhaps the reason Flash uses the Cosmic Treadmill to hop between worlds is because he requires it for the precision to not exceed the speed force barrier.

A being at this level theoretically has the ability to escape any fight by escaping to one of infinite other earths. This isn't conducive to winning a fight but is sure helpful in surviving one. It can also theoretically be used for dimensional bfr. 

One thing I postulate is that Superboy Prime's "retcon punch" was actually a punch that exceeded the speed needed to break the dimensional barrier and it causes a "dimension boom" as it were. 

Tier 0: God Tier: Beyond the Speedforce Barrier


The Final Barrier for DC Speedsters, the Speedforce Barrier.

If you take the fastest characters in the DC Universes, mortal universes, and they push themselves they can attain this speed. This is the speed of the Gods.     

Beings at this speed have the ability to transcend mortal universes and not only travel to other mortal universes but to the higher realms like Underworld or New Genesis at will. At this speed you can attain a limited omnipresence should you so choose because there is no longer an upper bounds to speed. Characters at this speed if they die, can come back from the underworld to the mortal realm via running/flying. Of course it's hard to kill them when these characters can outrun death itself. This is what the ultimate level of speed is in the DC Universe.

So yeah those are the levels of speed in DC Comics. Characters in the same tier tend to be represented as being about on the same level. Characters can generally at least react to people one tier higher then them, but 2 tiers higher and they are frozen. This is so you know who you can scale to who.