From my thinking, I would strongly encourage staying within Atmel’s 8MHz limit for the voltage you are running at.
The Arduboy offers a unique and interesting value proposition. It is wallet sized, can be reloaded with a standard USB cable, and offers a reasonable suite of capabilities within that range. But none of those items are valuable if you put the reliability and resilience of the device at risk. If you push the default setup outside that range, that is risk you are taking on.
The most successful of the early handheld game units did not achieve their goal with incredible graphics or high performance. You could probably deliberately run your bicycle over it without really affecting its operation. If games needed more performance than the device could bring to bear, then those games typically never made it to market, or you found a developer who could make magic without the high performance. Furthermore, if the device had been unreliable, or some units were flaky, this would have killed the reputation.
At the core of this, I think you have to decide who this device is for, in what proportion. If it is primarily for the type of people in this forum, then you can overclock it and expect that people who own it can deal. But if a significant fraction of owners will be people who will take the cable they have, and only ever load and play games and software, then I think you want to lean very heavily towards reliability with a conservative design. Right now, from what I’m seeing, you already have a pretty conservative design.
Those of us whose first reaction to a new device is undo the cover screws and pop the top off are one group. Those who first reaction is throw the power switch and play the game, and quite possibly never undo the screws, are another group.
One group will value:
- lots of connectivity
- lots of performance
- easy open case
The other group will value:
- good value for money
- always just works
Even with a conservative design, you still have an amazing design. The processor has an efficiency advantage of about six times more MIPS per MHz than a Z80. A classic handheld would run a Z80 at 4MHz for 0.58 MIPS. At 8 MHz you have nearly 14 times more processor power to run with. Insufficient performance will not be a limiting factor in the vast majority of cases. A solid community base will leverage what you are offering to achieve things you did you think were possible.
Although the cost of alternative cables in dollars is not a lot, the cost in time, effort, and attention for many people will be quite high. A standard micro USB cable can be replaced for a few dollars within a two minute walk. I can get them at the newstand! And if I have a sudden hankering to change games at work during lunch, I can likely do it, because there will be a spare micro USB cable there to charge my phone.
I think the ability to emulate a keyboard, mouse, or serial port is a vastly underrated feature. I am already thinking - and I doubt that I am unique - of a password manager, which can plug into a USB port and inject a selected password on command. Being able to carry such a device in my wallet is far better than carrying a card with all my passwords written on it. And again - the value of such a device plummets if the reliability is suspect.
Elsewhere here, I’ve written about trying to achieve peer-to-peer Arduboy communication and games. I think it would be very very cool. But it’s not as important as the main goals. If it can be achieved, great. If not, I’ll still have a small stack of reliable wallet sized game machines. To my thinking, that same logic applies to almost every “wouldn’t it be cool if” comment in here. Yes, it would be cool. But not as cool as reliability and target focus.
I think that the goals of resilience and reliability are key here, in a package that keeps value high and cost low by working with technologies we find around us everyday. Please do not succumb to the deadly infection that is scope creep. Stay on target, and deliver on time.