It has been noted that smaller logistical ships will be able to do express deliveries, as the smaller jump points that they can use are more convenient, and end up in a faster trip. In comparison, larger ships will need to make large detours. Also consider that you have to fill it up to make it worth your while, or you could specialise in expencive goods with a fast delivery rate. Either way, the game is being established so smaller logistical jobs will no be redundant with hte pressence of larger ships.
Just because the B is a smaller ship, do not think that it won't make a butt tonne of credits.
Personally, I think you are better off sitting on it for the mean while, especially if you are looking at the Star-G for pure trade. As I stated before, the base Starfarer holds considerably more, what I neglected to note is that it is also cheaper as well. If it turns out that you would prefer a Starfarer, wait for it to come in hanger, or when/if it comes on sale prior to that, and upgrade to it. This will preserve your LTI, which while not being all important, is nice to have on your bread and butter.