I just found out that REW has an SPL logging function. For example, below you'll see the 2nd set of cannon blasts towards the end of the 1812 overture. The Red and blue lines represent the Peak SPL (red) and Minimum Fast (blue) levels. The yellow is the Maximum Fast SPL. The black trace is the measured Fast SPL at the given time. These are dBZ values (z stands for zero-weight).