If latency would not be onerous, maybe you could create an instance of your app in Fly, and then wire it into your LB and DB. That should not be much work, and you then can look at CPU/memory/reliability metrics across the two providers.
Fly has had some teething problems, and a couple of hopping-mad customers, but the view from employees is that the brittle parts are giving way to more reliable replacements.
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