I did a few tests...
Going from Fort at York to Sardon's Tower took 1:12 by Mount at 5 Speed and 1:47 by Rail.
While Sardons to Snow took 1:08 by Mount and 0:52 by Rail.
So it really just depends on where you are going. I used the towers as points cu i figured that where people would want to get to and from the fastest. Going from York to snow by rail only takes about a minute. But by mount it would be closer to 2.