Oracle, did you have a chance to do any tests on accuracy when you ran the speed tests?
When I was doing the speed tests, I didn't know there was a prescaler for the ADC speed. I thought it was fixed for the chip. I didn't know running speed or accuracy tests on that part was possible.
It probably wouldn't have mattered to me since I knew my bottleneck was the LCD. And my project is working perfectly now with the timer interrupt library from playground, so I didn't actually need to speed up my loop.