How many trackdays have you done so far? Can you run a session of I without getting passed much? How comfortable do you feel about close passing? (6 inches instead of 6 feet in places you don't expect it)... 1:48 is fast enough, but getting passed by some of these guys (including current AMA racers) is a gonad-shrinking experience. This is my third year and only my second weekend in A. I ran a 1:43 last month and still was one of the slowest ppl in A. I would recommend you run in I and find a coach, ask him to follow you and if you are fast/predictable enough, ask them to move you up. Vacancies always occur because SOMEONE will crash out.