I spent quite a while learning how legitimacy/game mechanics work when I was active on Pokecheck (this was when I was learning to RNG abuse), so I went through a ton of recommended sites, including one that listed the exact
odds when using a pokeradar (the link is not the site I initially used, but it has the same info). The increase in chances caps at a chain of 40, so the best odds for the pokeradar is 13147/2621400 (a 0.502% chance) or roughly 41 times better than normal.
The Masuda method is fairly well documented as to it's effect (increasing your chance of a shiny roughly sixfold).
The shiny charm also increases the chance by a fixed rate and can be compounded with the Masuda method (although I've been burned more than once,
Serebii is actually right on this one)