Read https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-network-bandwidth.html
The available network bandwidth of an instance depends on the number of vCPUs that it has. For example, an m5.8xlarge instance has 32 vCPUs and 10 Gbps network bandwidth, and an m5.16xlarge instance has 64 vCPUs and 20 Gbps network bandwidth. However, instances might not achieve this bandwidth; for example, if they exceed network allowances at the instance level, such as packet per second or number of tracked connections. How much of the available bandwidth the traffic can utilize depends on the number of vCPUs and the destination. For example, an m5.16xlarge instance has 64 vCPUs, so traffic to another instance in the Region can utilize the full bandwidth available (20 Gbps). However, traffic to another instance in a different Region can utilize only 50% of the bandwidth available (10 Gbps).