STM32F103C8T6 is a very powerful Microcontroller and with its 32-bit CPU, it can easily beat Arduino UNO in performance. As an added bonus, you can easily program this board using your Arduino IDE.
 
Model: STM32F103C8T6.
Core: ARM 32 Cortex-M3 CPU.
Debug mode: SWD.
72MHz work frequency.
64K flash memory, 20K SRAM.
2.0-3.6V power, I/O.
Reset(POR/PDR).
4-16MHz crystal.
On-board Mini USB interface, you can give the board power supply and USB communication.
Size: 5.3cm x 2.2cm.