I know a lot of people say Python3 is slower.
I was reading a Twitter post (Facebook or similar) recently.of a large company who had moved.from Python3 from their Python 2.7 code.
The increase in speed and drop in memory usage was quite large.
Wish I could use Twitter better to actually find it useful and find a post again 10 mins later.
(While simple benchmarks for small code can be shown to be slower for Python3)
Anyway, move to Python3. Why not, may as well take advantage of any improvements they bring. Even Debian are doing it, the Stretch update from Jessie includes a lot of Python code having been updated to Python3.