The reason I suggest comparing against Python 3 is that Python 2 is no longer supported by the CPython project. Also, by far most of the people who start with Python will use Python 3.
If Python 2 is faster in many string benchmarks that's most likely because the default string type in Python 2 is simpler (just bytes) vs. Python 3 (code points). If you see your data as just bytes and want to compare on these grounds, compare with Python 3's `bytes` type. Now, when benchmarking Nim vs. Python, should you use a Python version and/or code style because it's more similar in implementation to Nim or should you use a Python version and/or code style because that's how most people would use Python? :-) By the way, I think it's similar to the question: When benchmarking Nim, should you use the fastest implementation or the most idiomatic/straightforward implementation? I guess it depends.
