Benny, I also have a MacBook, 2.2 processor, 4gb memory I just loaded 7 songs all with "Real" instruments.
All were 3 choruses long and the load times were as follows (in seconds)- 26,27,21,35,33,34 and one song that was "unfolded" that took 40 sec. That seems typical for most of my load times although while I am waiting it seems forever compared to the older midi versions of the same songs.
I also convert to AIFF for use in Logic and Garageband but I thought that was only a step needed so that those programs were able to import to Logic and GB. I do have to admit I don't completely understand that part of transferring songs or information from one program to another.

Ernie