8m/1sec x 1km/1000m x 60sec/1min x 60min/1hr = 28800km/1000hr = 28.8km/hr is the max speed of a minecart.
1,000,000km will take 34,722 hours just to traverse via minecart. Or, more precisely, thats 1446 days 18 hours 12 minutes 57 seconds. Just to travel, assuming the max speed of a minecart. You gots to build this thing son.
Maybe you should make it 1,000,000 meters. Just sayin'. Thats only about 35 hours by way of comparison.
So... Man i only wish you GOOD LUCK and i give you:
Well, I can say from experience that your computer won't crash at extreme distances... I just ported out to 1000000000000000000000 on the x coordinate. Clouds are the only thing that seem to exist here, and they aren't... normal. Normal movement, however, is impossible from about 12000000 on.
I do believe that you will be playing minecraft 24/7 for the rest of your life, with your wife feeding you sandwiches while you sit at your computer and go to the bathroom in a plastic tub. :~`,`,`,`,`,(
Actually, you CAN reach up to 12 million blocks, and even up to the billions, but at that point, if you don't have the greatest computer on Earth, Minecraft will inevitably omega-glitch and crash.
I believe the most you can travel is 2 billion 147 million and some other numbers. You can't technically -travel- out that far, since you will inevitably crash by the time you get to 12 million, but you can teleport there with SinglePlayerCommands. You'll only last about a second, though.
It is laggy, but not that laggy. My computer is average at best, and I do lag a lot at farlands, but was able to play around there without crashing.