I believe p.pfeffer is specifically looking for a way to display the response time metric from multiple servers on one GRAPH. I took a look at the new custom dashboard feature that was recently released. It does look like a powerful feature, but I do not see a way to combine the same performance from multiple sources onto one single graph. Like you mentioned, you can add the response time from multiple monitors on a single dashboard, but this is a completely different outcome.
Comparing similar data in a single graph/chart is much easier than comparing the data across multiple charts in my opinion.