So it wasn't so much that Ohio has worse performance, but that talking to services across region does.
One note on Firehose specifically for the curious - we make requests to Firehose in Ohio, and then Firehose sends the data to S3 back in Virginia (which we didn't want to move). Normally sending data across regions is expensive, but Firehose actually absorbs the cost in sending the streams to S3. We're honestly not quite sure why, but it worked out great for our costs!