I'm wanting to run the 1284P directly from lithium (4.2V peak, 3.7V nominal) with a LDO 3V3 regulator (dropout ~3.4V). Page 325 of the Atmel datasheet (http://www.atmel.com/Images/doc8059.pdf) shows the speed grades for the chip. My first question is to ensure I understand the graph correctly. Since it's linear it seems like a simple cross-multiplication to get the exact speed at a given voltage. If my understanding/math is correct...

2.7V @ 10MHz (given) 3.4V @ 12.58MHz (calculated for regulator dropout) 3.7V @ 13.7MHz (calculated for lithium nominal) 4.2V @ 15.55MHz (calculated for lithium peak)

The second question is that assuming the above is correct I understand I'll be overclocking a bit at 16MHz, especially as the batteries drain. Has anyone else done this? Maybe with a 328P and can let me know if things went well or they had problems? I feel like I've read that people have done this without any issue but since this is a small-run commercial product I'm working on I don't want it to be unstable.

Any advice here is appreciated -- thanks in advance!