Game Insight, which makes Android’s top-grossing app in the U.S., U.K. and Canada, said its hit title “Paradise Island” raked in $640,000 in net revenue this May.

This gives developers a sense of the current upper revenue bound on the Android platform — at least through in-app purchases and paid apps. (The top-grossing list doesn’t include revenue from offer walls or advertising, so there may be other higher-earning titles with ads such as Rovio Mobile’s Angry Birds.)

For comparison’s sake, it’s possible for a game on iOS to earn more than $3 million per month, according to conversations we’ve had with leading third-party advertising and analytics providers and top developers.

So with these assumptions, we’re looking at a 5:1 ratio when comparing potential run-rates on both platforms for a single game right now.

This is pretty consistent with what we’ve heard from other developers. Earlier this month, Glu Mobile said its Android portfolio of games was making one-eighth to one-tenth of what its iOS titles were making. The company’s chief executive Niccolo de Masi also told us that he anticipates that the company’s Android apps will make about one-half of what its iOS titles make by year-end.

Moscow-based Game Insight said the app broke 1 million installs mark in the title’s first three weeks and now has 3 million users, according to company manager Vera Konysheva. The game is a classic casual sim title, where players build and manage a resort where they can earn revenue from pleasing virtual tourists.

The game monetizes through in-app purchases of virtual currency which can speed up actions in the game. It’s classic social-gaming style monetization, which only became recently possible on Android Market thanks to Google’s launch of in-app billing at the end of the first quarter. The Moscow-based company has about 200 employees and 11 studios. We’ve reviewed a few of their previous titles here, including MyClinic and The Syndicate HD.