You can switch to an r5.xlarge, which has the same amount of CPU but twice the RAM. More on reddit.com

This is a nonsense question since we don’t know your app but the nonsense answer is unless it’s a legacy monolith I can’t think of too many scenarios where I would not rather four behind load balancing. It affords maintenance, updates without a window of downtime. More on reddit.com

The baseline performance of a T instance is less than 100% CPU. T series instances are designed for "bursty" workloads. Basically your CPU is shared with a lot of other people, and the baseline performance and bursting are there to prevent anybody from using too much CPU (unless they pay).

An M5 instance is basically "bursting" all the time for free. You can use 100% CPU for as long as you want, at no additional cost. The CPU is dedicated to you.

A T series instance is indeed cheaper if you stay below the baseline. (If you do not enable T2/T3 unlimited, then the instance will be throttled, if necessary, to keep it below the baseline.) But if you run 100% CPU for extended periods, the T series instances are actually more expensive and you would do better with an M series instance.

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The 2 differences that stick out to me with T3 instances and pretty much anything are (a) the burstable credits you mentioned and (b) the networking. T3 network performance is capped at 5 Gbps regardless of size while M5a are capped at 10 Gbps unless you run a 24xlarge with Enhanced Networking for 20 Gbps. I don’t think T3 even have an “Enhanced Networking” capability. Additionally, M5a have the dedicated EBS throughput in additional to their normal networking traffic while, I assume, the T3 treat EBS traffic just like all other network traffic. That makes the network throughput even worse on the T3. More on reddit.com