About the only effect would probably be how quickly the cash comes in, unless its a fixed amount over a number of turns and not dependent on the frieghter arriving at your world.
and I think the faster the frieghter, the more turns it can stay on that route? I'm not sure about that.
edit:
| Nope. All freighters have a speed of 1 once the route is established. |
really? I don't know much about frieghters then since I don't use them much in the demo (because its only 3 years game time, it doesn't feel worth it and I want to do other stuff with the demo)