Alex
A few things to add/implement to what has already been said:
1) use the tools you know, don't experiment during a wedding, especially if you're paid.
If you're more confident with DSLR, go with it, D700 (I have it) is really great for low light and has also a kind of RF mode (using FX lenses in DX mode) which I find very useful sometimes; go with the RF only if you can really master them AND it won't steal you precious time if you're already shooting something else.
2) Make the bride and her mother happy and they will be your best "ad" among their friends.
3) Here (better, in Southern Italy) we use a "supplemental day", usually BEFORE the ceremony in which the couple may play and experiment whatever they want with more time and less stress.
During this day, called here "anteprima" (you would call it "preview") spent in a place which is somehow meaningful for the couple or pictoresque photographically speaking,
photographer and the couple may work together not only to get more posed or natural pictures depending on the couple's likings, but also learning to "cope" one another and have more time to think of pictures to do for the wedding day.
I really suggest you to ask the couple to have - for the same price or a small add - a day out with you. They could be pleased and surprised by this offer and could get the "plus" you're offering them.
4) I agree to ask the couple if they namely require or like "film" in addition to digital shots. Maybe they won't but at least they will know you thought of it as an alternative choice.
Last but not least, if you really master RF, although it's indeed more challenging (due to the limited focal lenght range, especially on the tele section), by any means use it especially during those moment in which flash isn't allowed (i.e. - I think of a catholic mass here, during homily or bread / wine blessing or the common prayer of the "Our Father" when often people give hands one another or turn them to the sky)