In my humble opinion I do not think that you would ever be able to detect any country specific biases as I believe they are very careful to process all applications in similar matter and even if they would be able to process an application from a specific applicant faster than from another, I believe they make very sure that they let the one from the former applicant sit to not make this obvious.
For what it is worth: when I applied for permanent resident status for Canada while living in the UK, being married to a Canadian, with three Canadian kids and married for then over 17 years it took me exactly six months to get the permit, the same amount of time it took everybody else, even though I believed that I had a slight "advantage" by my marriage to a Canadian and being a German passport holder, with assets to bring into the country. I can assure you I had no faster processing time than any other applicant. In fact: they said it would take 6 months and it took to the date exactly six months.
I think the variations in time have more to do with different citizenship offices than with where we come from and as said, should there be differences in our countries of origin I am sure they make very sure that we would not know this.
Stef.