Payment reminders

We are currently deciding on a system for automatically sending payment reminders to clients with unpaid invoices and it would be interesting to hear experience from others how you deal with this aspect. One of the challenges is that we have multiple different versions of such reminders depending on how much time passed since the due date while XTRF allows (AFAIK) for only one email template of the type "When client is reminded about a delayed payment". This could be probably worked around by putting some if/else code into the template that will allow for using more versions. Then we are thinking of a macro that will periodically run and sent the above reminder for all invoices with given delay since the due date.

Any tips or ideas you can share how this can be handled efficiently?