Apple is most definitely not going to reveal the split up between the iPhone 6 and 6 Plus sales numbers, probably for ever. We can wait for the analysts to play around with the numbers and reverse calculate the split between these two models, based on the profit the iPhone earns this quarter and its average selling price. Or we can look around for some usage analytics data, like this one, from Applovin.
No surprises here. Of course the iPhone 6 Plus seemed popular in the beginning because Apple sort of under estimated the demand for a humungous iPhone, mainly in the Western countries. But the more iPhone 6 Plus owners I talk to, who did not plan to purchase a 6 Plus originally, the more I am convinced that people love it. Be it our craving for having the best iPhone or bigger the better (like in buying TVs, for example) attitude, the 6 Plus has ended up in more pockets in the Western countries than expected. But overall there was never any doubt that the iPhone 6 will clearly outsell the 6 Plus, the questions was by how much margin and the most common number that has been floating around was, for every iPhone 6 Plus sold, there were three or four iPhone 6 models sold. And that seems to consistent with many studies so far (another one on this from John Gruber, here).
And the 6 Plus is more popular in Asia than the West, due to either weaker purchasing power in Asia, requiring consumers to choose between a smartphone and a tablet and/or that Asians, in general don't want too many gadgets, lying around in their household.