To get an estimate of your potential performance you can run the Backblaze speed test here: https://www.backblaze.com/speedtest/
Keep in mind that to achieve the best speeds, you may need to incorporate multiple threads into your script.
Currently, a single thread should be able to upload or download at about 30 - 50 Mbits/sec. You can achieve much faster speeds if you uploads files in parallel using multiple threads. We have documentation with sample code for uploading files in parallel here.
Note - The first time you request a file, it needs to be requested from the Backblaze Vault it is stored on. This will add 20 - 100 milliseconds, depending on the size of the file. Subsequent downloads of that file will be cached and return at wire speeds, up to 5-8Gbps.
Please also be sure to consider latency
Currently we only have one datacenter located in Sacramento, California. By running "ping f001.backblaze.com" from your terminal or command line interface. This will give you an idea of the latency between your location to our datacenter.