Here are a few performance numbers for the ESP8266 breakout running Arduino IDE sketches.
sparkfun thing dev
speedTest numbers from old UNO sketch
Teensy3.1 DUE ESP8266 ZERO CC3200
96mhz 84mhz 80mhz 48mhz 80mhz
nop : 0.010 : 0.012 : 0.013 : 0.021 : 0.013 us
Arduino digitalRead : 0.146 : 1.033 : 0.527 : 0.901 : 0.576 us
Arduino digitalWrite : 0.466 : 1.263 : 0.430 : 1.366 : 0.436 us
pinMode : 0.238 : 3.068 : 1.472 : 1.938 : 2.956 us
multiply volatile byte : 0.062 : 0.118 : 0.100 : 0.201 : 0.100 us
divide volatile byte : 0.088 : 0.138 : 0.402 : 0.606 : 0.101 us
multiply volatile integer : 0.062 : 0.083 : 0.148 : 0.168 : 0.074 us
divide volatile integer : 0.068 : 0.093 : 0.447 : 0.906 : 0.081 us
multiply volatile long : 0.063 : 0.083 : 0.148 : 0.168 : 0.074 us
multiply single float : 0.456 : 0.903 : 0.735 : 2.796 : 0.979 us
multiply double float : 0.686 : 1.158 : 0.860 : 4.183 : 1.204 us
divide double float : 11.923 : 19.118 : 9.997 : 43.546 : 20.971 us
random() : 0.373 : 1.368 : 4.498 : 9.771 : 0.571 us
bitSet() with volatile : 0.052 : 0.070 : 0.110 : 0.124 : 0.074 us
analogRead() : 8.448 : 39.543 : 384.497 : 423.096 : 8.596 us
analogWrite() PWM : 1.678 : 3.508 : 10.497 : 8.291 : 6.186 us
I had to sprinkle in some yield() calls and reduce some loop counts to avoid WDT reset.
From the IDE, you can select 160Mhz, but that seemed to only speedup the NOP loop ??
Here are some more anecdotal comparative performance numbers.
On my local wifi net, testing to a wired Ubuntu box, I measured the following network performance:
ESP8266
ping rtt min/avg/max/mdev = 0.832/0.967/1.093 ms
TCP send: 0.28 mbs receive: 8.6 mbs (sending or receiving 1000-byte records)
UDP 8-byte echo RTT: 716us (though more than 1 second after a delay() ?)
UDP send: 28 mbs receive: 30.7 mbs (1000-byte packets)
-----------
CC3200
ping tt min/avg/max/mdev = 19.213/80.313/139.361/30.570 ms
TCP send: 12.6 mbs receive: 2.8 mbs
UDP echo RTT: 2146 us
UDP send: 1.8mbs receive: 86mbs (breaks packets into 255-byte packets?)
-----------
WINC1500 (SPI clock 12MHz)
ping rtt min/avg/max/mdev = 5.282/7.151/16.072/2.897 ms
TCP send: 3.3 mbs receive: 2.8 mbs
UDP echo RTT: 2421 us
UDP send: 3.9 mbs receive: 3.4 mbs (large recv buffers?)
Your mileage may vary. (mbs is megabits/sec)
On ESP8266 I could not send more than 5 back-to-back UDP packets. Also ESP8266 UDP won't send packets larger than 512 bytes unless you hack pbuf_unit_size in UdpContext.h
Also see comparative SPI performance and wiznet speeds
I don't know the specs of the 26MHz crystal on the Sparkfun board, but its frequency is only off by -25 ppm (spec is probably 30ppm). In run loop with USB power, I measured power consumption at 29ma. With wifi active, power consumption is 90ma, with higher peaks.
EDIT: added CC3200 and WINC1500 data