[passive]

I've been writing mostly small python projects for 15 years, starting with 2.2.

I've had no issues in the migration to 3.

I did some building with it around 3.3, starting to commit around 3.4, and with 3.5 I build everything in it.

I don't have the performance challenges Instagram has, but my experience with application development in general is that 98% of performance challenges can be solved with (not-too) clever engineering. This applies to projects in every language.

There are a vanishingly small number of scenarios where the performance of your runtime actually dictates your performance limits.

If you're working on something and are worried about Python's performance, or which Python to use, don't. Use 3, optimize later.