Had a chance to get out this morning and do a little testing with the Sony A7RIII and the Sony A7III with my style of shooting. This is in no way a scientific approach to testing these two cameras but it's my thoughts on how I think they performed based on my shooting style.
First a few key differences between these two cameras
Price - Sony A7RIII ($3200) is around $1200 dollars more then the A7III ($2000)
Effective Pixels - Sony A7RIII (42mp) vs A7III (24mp)
Focus Points - Sony A7RIII (399) vs A7III (693)
Viewfinder Resolution - Sony A7RIII (3.7millon) vs A7III (2.4millon)
LCD Resolution - Sony A7RIII (1.44m) vs A7III (922k)
4k Video - In 24/25fps Sony A7RIII (5k down to 4k) vs A7III (6k down to 4k)
Buffer - Based on MP the A7III can buffer a little over twice the amount of JPG and around 13 more raw files - Both shoot max of 10FPS
Weight - Sony A7RIII 657g vs A7III 650g
Sharpness - Sony A7RIII has no low pass filter so is slightly sharper vs A7III which uses the filter to reduce moire patterns
Both have very similar size and weight and though slightly different was not really noticeable to me, Both of them use the new Z type batteries which are amazing and I am getting the equivalent of between 2 and 3 original FW battery times out of the camera, and both have dual card slots.
A few examples of before and after with each camera. Setup was tripod with the 24-105, same settings, focus, WB, etc. They are not perfect by any stretch but close enough.
I will also upload the higher resolution images to the following location to check out.
Wake Up Early. Drink Coffee. Never stop chasing the light and always get out there and shoot.