Pardon me if I'm inserting myself into the conversation here, but about the two frames of references...
From an observer that is accelerating upwards, being pushed by a flat Earth, time will always appear to move forward at normal speed. It's only from the outside that general relativity would make them never hit the speed of light. What you FEers don't seem to realize is this model would limit the existence of the Earth to about a year.
So, if the speed of light is 299,792,458 m/s then after 30,591,067.1 seconds, or 0.969393125 years, (a year, basically) you will have hit the speed of light. Besides asking where the infinite energy required to reach that speed comes from, you must know that if the Earth acceleration theory for gravity were true, after a little less than a year an infinite amount of time would pass on the outside, which breaks the universe.
So, if no one was here on Earth to observe it accelerating on the inside, the theory would be valid, since no one would ever survive an infinite amount of time to see it reach the speed of light. But since we are here watching this theoretical disk accelerate, the fact that the planet has been around for millions of years, and humans have observed it for thousands, and that we ourselves have existed for more than a year, disproves the acceleration theory altogether. Does this make sense?
You flat Earthers need to come up with another explanation if I am right.