Hyper-band access by ship type
Hyper band access. The upper bands of hyper-space are obviously a nasty place to be, and apparently military-grade hyper generators are required to reach the upper ones currently utilized, yes? The questions in this thread, I think, are (a) whether or not size is also a factor (do couriers use the highest bands because they're small enough to get there, or because they're small enough to lose if you have to); (b) are courier crews specially trained/equipped to use those upper bands; (c) is R&D to crack the barrier to the bands which are currently completely unreachable underway, and are there any hints you'd like to drop as to how said R&D might be progressing.
I don't have the tech bible in front of me, so I can't give you exact numbers and values (as if I would if I could [g]). However, in the most general terms.
(A) Size is not a factor in how high in the hyper bands a ship can go; it's simply a factor in how high a navy is prepared to declare that a ship will go. The dispatch boats and courier vessels used by navies and interstellar news services in the Honorverse are small enough, and carry small enough crews, that their possible loss can be balanced against the advantages of faster transmission of critical messages and news. In Honor of the Queen, Alice Truman decided that the news and dispatches she was carrying justified the possible loss of a light cruiser and its entire complement, but those were extraordinary circumstances. Mind you, under similar circumstances, an admiral might very well order a destroyer, or a cruiser -- even a battlecruiser -- to follow exactly the same flight profile Truman used. That would be, however, a "hostilities-only" type of decision, not one which would normally be made in peacetime.
(B) Courier boat crews do receive additional training before they're assigned to the duty. Their equipment is essentially the same as any hyper-capable ship's, except that it is maintained within much closer tolerances. There is a certain amount of "play" in hyper generators and [inertial] compensators; that's why a ship with a particularly good engineer can afford to push its compensator harder and cut its safety margin thinner than a ship with a less skilled engineer. Courier boat engineers are highly trained, and their generators, compensators, and nodes are overhauled at least twice as frequently as those of ships which will not normally be operating as high in the hyper bands as they will.