BTW, trying to figure out the reason of your question I can say that templates usually DO NOT impose any performance overhead at all. You won't lose anything. Most of the time, templated output will even speed you up by itself, because there's buffering, there's precompiling and all that staff.
You are right, that was my main concern. That by using templates I would get a hit in perfomance. Specially when using CGI's that generate dynamic content.
Thanks
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I've found that using TT does impose an overhead on CGI scripts, because every time the TT modules have to be recompiled, etc, which might take around 0.2 s (depends on the machine). But if you use mod_perl or speedycgi there is no problem.