The Teensy 3.2 might be a good option if you need that Micro/Mini form factor. 32 bit, standard clock speed 72MHz, 8 times more memory, 12 bit ADC and a DAC pin.
If you manage to exceed that, then the Teensy 3.6 is available on Kickstarter right now. More like a Nano form factor but heaps more functionality.
All Arduino code runs on the Teensy, unless you've used AVR-specific features like direct port writes. With the higher clock speed of the Teensy, digitalWrite() works faster anyway.