I'm soliciting recommendations for DNS based load balancers. Currently, we have Cisco Global Site Selectors deployed buy have reached a limit for the number of active HTTP HEAD checks we can perform. This lack of scalability is restricting us severely with regards to the number of customers we can deploy for our product, which requires a separate HTTP HEAD check per IP per customer. I am hoping to receive recommendations for devices which allow for DNS based load balancing (round robin and proximity based) as well as HTTP health checks (including content based health checks). It must be scalable to, at least, 2000 active checks and active answers. I am currently investigating the Netscaler DNS offering as well as F5's 3DNS (or whatever they've changed the name to).