I have now repeatedly visited this thread and your question is good thinking material. I think it merits dicussion and was hoping someone else would post here.
But since no one does… I will.
First of all I find that the comic medium is quite different than the movie. With only stills you are forced to make all of them pretty and completely functional where in a movie you have the option to play with one or the other. Reading your post I still come back on this thought.
Next up the scenes. I have no feel for how long your story is but with most comics weighing in at about 32-48 pages (american an european standards- could be wrong its out of my head) I think that exposition on page 3-6 is rather late. To fully capture your audience you have to persuade them to read the next page over and over again. And unless those first two pages are really important I would try to jumpstart the story on page 1 or page 2.
Which is why you see that a lot of comics have A) a lot of frames and wall-to-wall text or B), exposition all lumped into one frame.
It is to get the reader through that as quickly as possible and into the story. Best case scenario is setting the scene in the first page, having a first shot of the main character as the last panel and character introduction and exposition starting on page two.
Basically in comics the more panels a certain scene gets, the slower time and story goes. That is a real good rule to keep in your mind as you are pacing your story. And ask yourself a question where do I want a slow and dramatic feel and where is the quick camera motion and action.
If you want to take setting the scene, character introduction and exposition slower. You have the option to make small stories of those particular scenes and extending them to an 8 pager for example, something that is quite often done in american comics that run as a series.
Having character introduction and background as story elements (cutting it up and mingling it with your main storyline) is another technique you could use. Long scenes become short but recurring and it is a good way to keep attention, build anticipation and tell a little more about a character or place.
Final thoughts: I personally don’t think 2.5 pages is too long per se. But it is dependent on how long your overal story is and if the reader still would want that extra information and turn that page to get to it. As long as the story doesn’t get boring nothing is too long.
But like in all writing you have to be very self conscious and kill everything that hasn’t a specific purpose. If you don’t get away from a project, look back at it with fresh eyes and a red pen in hand everything will eventually become too long and boring.
Please share your thoughts on the issue.