Hi seimi,
I don't have a pic of a Q with the Russian Turret, but if you go to this site which has about the most comprehensive info on available accessory OVFs on the 'net that I've found:
Leica View Finders
you can get an idea of scale of some different OVFs from the pic at the bottom of the page. Obviously, the Nikon SP is significantly larger than the Q as it was a 135mm rangefinder. I'd estimate the Q is about 2/3 the size of the SP in width from comparing images of both cameras using the flash shoes as a reference.
Hope that helps.
Scott