When, about a decade ago, I discontinued saying the Novus Ordo in Latin and resumed the Tridentine Mass, I deemed it dignified and logical to keep what I did in line with the calendar of the Devon churches which I served, and, not least, with the admirable Broadwood Widger, where the PCC had retained the Prayer Book. So what I generally did was this. When resuming the mass of a Sunday after Trinity on a weekday, I hopped about a bit in my Missal and, for example, in the week after Trinity 10, I said the mass of Pentecost 10, except that I used the Collect (etc.) and Gospel from Pentecost 9. I carelessly used the Novus rules about commemorations and when to use the Gloria. Some Prefaces from the Conciliar rite got gummed in. I also used the Tridentine Sanctorale propers on the days indicated in the Novus Ordo calendar (as, I believe, some RC clergy did, particularly on the South Coast).
Currently, I am using the St Lawrence Press ORDO, the Calendar being that of 1939. This means that I rarely have to face the problem of which Sunday mass to say on a weekday, because nearly every feria has something on it which must or might supersede it!
But, at our Sunday High Mass, Novus Ordo but avoiding ICEL translations of the Latin in favour of the renderings by Cranmer and the English Missal, I use the Prayer Book Sunday collects on the Prayer Book Sundays.
Of course, you will say that this is just the old Anglican weakness for picking and mixing to suit ones own whimsies. But as for the question of using the OF calendar when saying the EF in a basically OF church (and vice versa), this is something that PCED should sort out. There are real questions here of what is decent and edifying pastorally.