After using cheetah and mako at their functional minimum (only for substitution) for sometime, I started asking myself whether just using string.Template wouldn't be the better and simpler approach for my use case(less deps). 
In addition I wondered whether it would be reasonable to import these templates as .py files to avoid .open() on each call. This would make handling templates a little more complicated but other than that I'd save a lot of system calls.
What do you guys think? 
I'm well aware that my present templating is speedy enough for 99.9% of the use cases I will go through.
Thank you for any Input
After lots of trying and reading I found string.Template from the Core Library to be the fastest - I just wrapped in my own simple class to encapsulate the file-access/reads et voilà.
Fastest way to do _simple_ templating with Python