Hi gb

Earth's eccentricity, e, is about 0.0167. If a is the semimajor axis and the average speed, u = sqrt[GM/a].

Then the velocity at perihelion is:

V = u*sqrt[(1+e)/(1-e)]

and at aphelion is:

v = u*sqrt[(1-e)/(1+e)]

Thus v/V is (1-e)/(1+e), which in this case is 0.967. Not a big difference, but when propellant mass increases exponentially it can translate into a lot of payload.

As I understand it the Interplanetary Highway would use a series of Lagrange Point maneuvers - first the Earth-Moon L1, then the Earth-Sun L1 and eventually the Venus-Sun L2. I've no idea what the difference in propellant would be, nor the travel time, but as it can take months to do the EM L1 to ES L1, well...

Adam