The performace issues related to the transaction log (and data files as well) I have seen are related to the autogrowth. Now I tend to create databases and log files big enough so the autogrowth process does not occur.

I did run some tests where the maximum duration of some SPs calls was affected by the autogrowth process. The overall average duration does not get affected much, but on a system where you need to keep the maximum duration of a SP execution in check it could cause a problem.