Go Teensy instead.
No, it doesn't run on an Atmel, but it feels like the bravest Arduino. While it runs on 3.3V, it can handle 5V on pins.
In fact, it has so much more potential. Better bootloader, that does not require you to break connection before uploading. More pins with more versatility, much more RAM, a lot more speed. Multiple serial ports, multiple I²C, CAN out of the box are other features you get with the Teensy.
Don’t stop there: add a battery and a quartz and you added system time to it. Add a Wiz820io and you have networking. Add a SD and you got a hard drive. Breakouts to adapt are widely available, and code to make it all run is free.