Google Maps JS API; Plotting thousands of points

We're using the Google Maps API in JS to plot 5,000 to 20,000 circles on a map and as expected it's slow. Using markers seems to be even slower开发者_开发问答. If we were to use markers, we'd need to replace the marker with a transparent image.

What advice do you have for handling thousands of markers/circles on Google Maps?

I'm facing this as a potential problem myself - and from my research it appears that using a clustering library may be the solution. Here is an article comparing some solutions w/benchmarks - it is somewhat dated, but it might be the right jumping off point:

http://www.svennerberg.com/2009/01/handling-large-amounts-of-markers-in-google-maps/