Honest Question: Why not launch your app's infrastructure on both platforms and then round-robin your traffic between the two for a billing cycle and compare the results at the end?
If you are working towards "best practices" on AWS, you should be running multi-region (who wants to be the one left holding the bag when US-EAST goes down again?). If you've done all the heavy lifting to enable yourself to run in "pods" across mutliple regions.
Well, if you can do that, why not treat Linode/DO/Rackspace as a separate region and deploy a "pod" of servers there?
At the end of a month you should have enough statistics that are directly applicable to your own app and your specific customers, as well as some real experience with the operational experience of dealing with the new provider.
For example, maybe one of the other providers has really fast machines and their major upstream provider has a great peering relationship with whatever test node you were using for these microbenchmarks, but perhaps those servers are really flaky and crash all the time, or perhaps the majority of your customers see really bad latency when hitting those servers? Maybe their API isn't just "immature", maybe it crashes a lot and they have bad customer service.
Those are the sorts of things you aren't going to figure out after simply running a few load tests. Anyhow, it just seems like something like this would be a lot more valuable than any amount of synthetic testing.