Seriously - Most. Favorite. Thread. Ever. I love the large large large three stone look. Chrono & Packrat both of your rings have been saved as favorites of mine for awhile.
Uppy - not sure if this will help you my three stone are all three same color. But they are 5.5 x 6 x 5.5
The setting will make a difference on the coverage. If it's set at the same height, or side stones lower, etc.
Mine are the proportions you mentioned originally: 5,6,5. Actually the middle is slightly bigger at around 6.3. They are set the same height and here it is on my 5.25 finger. For larger ring size, love TL's ring and proportions (and the color mix too!)
I have a 7.5 finger, center stone is 2cts which I believe is the same size as a 1.25-1.5 diamond but cannot remember how big mm wise it is, .3 (each) sides. It takes up my entire finger.