I thought the AVRFREAKS crowd would like a couple of recent blogs we posted. Bonus points if you spot AVRMan!
The first one was a match-up between that AVR Mega and the PIC16 here https://www.microforum.cc/blogs/entry/47-comparing-raw-pin-toggling-speed-avr-atmega4808-vs-pic-16f15376/
The second one was a comparison between various Arduino boards here https://www.microforum.cc/blogs/entry/48-comparing-raw-pin-toggling-speed-between-arduino-platforms/
We are planning on doing a comparison of interrupt latency next, and who knows what after that :)
Take a look around the site as well, may just be something else that interests you.