I can't see any major problems with either combination, FD on PT or PT on FD.
Virtually all Citrus scions are more vigorous than FD, and most more vigorous than PT. They are overall both successful rootstocks.
There are various strains of PT, some more, some less vigorous, so you could investigate those if you are concerned about rootstock / scion growth differences.
Also small flowered and large flowered strains.
The fast flowering trifoliate, as suggested above may be a good choice.
PT has great autumn colour, some nice oranges and reds. Some seedlings seem to colour and hold colour earlier and longer than others.
Also remember that as a bonus, if the scion dies, your customer will still end up with a Poncirus in the end.