Sorry, never could really get enthused about the overworld rail. If the rail is under ground then stone is not an instant break block(except with haste 2 and eff5 pick), you need iron and gold for rails or a dimension of 3h by 2w to have any tolerable mode of travel,new players will not usually have access to iron mine carts or horses/saddles, it takes 8 times as long to travel in the overworld when compared to nether travel, and if it is all done in vanilla then the overworld rails would take a considerably larger amount of time to finish compared to a network of tunnels dug in the nether.
I am not trying to down the overworld rail idea or anything....but in my opinion, I just think the nether would be an easier,efficient, and faster solution. A 2 man team side by side can dig a 2 by 2 tunnel in the nether as fast as they both can walk. May be faster if you can dig it out while sprinting with speed pots. The 3rd layer needed for a horse path can be dug out on there way back to the start.
You walk at 4.317 m/s, sprint at 5.612m/s, and increase that by 20% if you can use speed potions while digging it out.. After 10 minutes of walking while digging with no speed potions and not counting time for food breaks, you would have dug out an approximate 2590m long 2 by 2 path(if my math is right and you don't run into random lava blocks). 2590m in the nether would then put you around 20720m from were you started in the over world(if my original math is right). plus you would use only around an 1/8th of the amount of rails if you decided to turn it into a rail system.