The "SIMD" instructions available are only 32 bits wide, a few 2x16-bit and 4x8-bit operations. The frame buffer returned by the getFrame() function is in the DTCM tightly-coupled memory area, so you wouldn't gain anything by using a separate working area and blitting your data over.
But yeah, I'm also seeing 48 fps drawing random static but the profiler says it's spending most of its time idle. 
I'll look into it!