Original Thread here for comments and supporting claims
Universal Disclaimer:
After spending months researching this particular wiki, I have become fully aware that what I am about to post may not be the most popular opinion. While I am not trying to accuse anyone here of unchecked bias, I have noticed the prevalent inclination to deem Superman feats outliers (even with numerous other feats backing them) while simultaneously allowing other feats from other characters to be added immediately and seemingly without the same evidence required for Superman.
With that said, and as I respect the opinion and intellect of many members of this wiki, I am asking that posters only respond with refutation of my claims after providing a clear explanation for why they disagree as well as concrete evidence they have researched to the contrary. I am not requesting this to be pompous or arrogant, but merely to get to the truth of the fiction we all love, which is ultimately why fiction exists in the first place. What you do here may not seem like it has any meaning or bearing on the real world, but keep in mind that every scientific marvel and advancement throughout modern human history began in a book.
"That's what fiction is for. It's for getting at the truth when the truth isn't sufficient for the truth." -Tim O'Brien
Introduction:
This is a Post-Crisis speed feat from the Final Crisis storyline for Superman of New Earth, Overman of Earth-10, and Captain Marvel of Earth-5 that has them completely outpacing and destroying the "Reality-Blitzing Missiles" theatening to destroy the entire DC Multiverse. Basically, the multiverse was being threatened by Mandrakk the Dark Monitor (a being from a race so large that entire universes are microscopic to them) with his goal being to "sterilize" and wipe all life of the entire multiverse, absorbing each and every individual's life energy into himself. Superman calls the Monitors a race of vampire gods, which is a very fitting description concerning the overall plan.
The Threat:
Below, I will first prove that these missiles were, in fact, intended to destroy entire universes, as stated by the comic issue itself and DC's official release of their Multiversal Map, which gives a description of the Monitors' ship classes.
Something to mention is that the terms "world(s)" and "universe(s)" are often used synonymously when talking of the DC Multiverse within the comics themselves. After the Infinite Crisis storyline, the DC Multiverse was compartmentalized into 52 known universes, which is what Superman is referring to in the above panel concerning the impending danger.
Next, the missiles being talked about are stated to be "Reality-Blitzing Missiles," which gives them a relatively fast sounding speed connotatively. The definition this site gives for a speed blitz is "the act of attacking their opponent before they are capable of perceiving or reacting to them." However, even though the whole ordeal is actually stated to take place in the time between a heartbeat, I will be giving several different time spans to accurately prove the speed of this feat.
The Feat:
Below, you will find evidence for how large a single DC universe is, the feat itself, and how long it supposedly took.
According to Post-Crisis Adam Strange, after taking Superman into the far reaches of space, a single universe in DC Comics is at least 100 trillion light years across (it is certainly more, but this is the only concrete statement currently available without relying on conjecture). Using that distance and the fact that these missiles were going to wipe all life in the DC Multiverse at a very rapid rate (blitzing reality), we can lowball how fast Superman, Overman, and Marvel had to be travelling to stop them. I say lowball because they were going to blitz through the entire multiverse, not just a singular universe.
And while the issue said they blitzed the "reality-blitzing missiles" in between a single heartbeat, I will be giving three separate distinctions for their speed.
High-End (what the issue implied)
100 trillion light years per 1 second = 3,155,692,600,000,000,000,000 c (3.15 sextillion c)
Middle-End (assuming the missiles would take an hour to cross the universe)
100 trillion light years per 1 hour = 876,581,280,000,000,000 c (876 quadrillion c)
Low-End (assuming the missiles would take a day to cross the universe)
100 trillion light years per 1 day = 36,524,220,000,000,000 c (36.5 quadrillion c)
Outlier?
It must be noted that this is toward the end of Post-Crisis Superman's career from 1986-2011 (before his reintroduction in Rebirth). Superman's specific storyline for Final Crisis took place in 2009 and wasn't contradicted as an outlier either before or after the feat. Actually, it's the contrary.
Four years prior in 2005, Superman performs a flying feat in Infinite Crisis from Earth to Krypton (located in the Andromeda Galaxy) in under five minutes that places him billions of times faster than light. If anything, this feat is just a solidification of Superman's growing power, as he's always been a character to grow in power the longer he lives under a yellow sun.
Reaction and Combat Speed
As you can see from the scans, they didn't just catch up to the missiles; they also encircled them before making contact (as evidenced in the middle missile that Superman destroys) using a rolling scissors maneuver often employed by fighter pilots with ships that have similar speed and thrust capabilities as their own.
To perform such a maneuver at such high speeds, the pilots (Superman, Overman, and Marvel) would have to be reacting to the very complex movements their trying to perform. Thus, the feat does not just qualify for travel speed, but also reaction speed as well.
Final Tally
100 trillion light years per 1 second = 3,155,692,600,000,000,000,000 c (3.15 sextillion c)