Why did you feel that you needed to start using Python in the first place? Do you have prior programming experience? Regarding data munging, that's sometimes a significant part of the CV/IP process.

Personally, I love Python. It's been working fairly well for our ML projects utilizing scikit-learn to process fairly large spatiotemporal datasets (temporally varying 2D and 3D datasets). I find numpy to be critical for keeping runtimes reasonable.

Regardless of the language, profiling may be necessary in order to obtain acceptable performance.