Picture Cache Max to constrained

I would like to be able to raise the picture cache max.
 
In my workflow, I record 16 tracks for 3.5 hours.
 
I select ranges, split, bounce to clips, and copy to new project. To select the range, I have to be able to see the wave forms.
 
I then create smaller one song projects and copy the clips into them.
 
I work across many of these little projects, but periodically return to the big project to get another song out.
 
When I do, I always have to wait as 3.5 hours of wave forms regenerate.
 
So I go to up my cache size and the max is 2 GB or so. Why can't I have a 20 GB cache if I like?