I am planning to run scripts to copy S3 files from one bucket to other bucket in same region( same account and different account - both cases are there). I am using Python scripts and running on EC2 instance. 
1) Will the performance depend on EC2 server type?
2) What is the best way to improve performance when copying S3 files from one account to another ( and also one bucket to another in same account, same region) . Given they are in same region and different regions. File sizes are around 1 GB each with total size of 5TB
Thanks
tom
Let me know if you need any other information.
No, in this instance the type of EC2 will not matter because you are using the AWS network to transfer data from 1 bucket to another. If you wanted to spin off parallel processing of the data (Run multiple s3 cp at the same time) then you would choose a specific instance, but in your case a T2 Small would do just fine.
aws s3 to s3 copy using python script on EC2