We print quite a number of 10’ viewing distance backdrops at 35-50ppi, though we recommend about 75ppi for small venues. For video or TV, we go the other direction and drop to 25ppi and intentionally put a heavy blur on the image.
It shouldn’t matter what the drop looks like to the people onstage. It’s all about what it looks like to the audience. Sometimes not even the front 3 rows of audience, depending on the size of the venue.
Print out a chunk of it (tile it if you have to) and tape it to a wall, and step back. Or get a printers proof of a 36" x 36" section if you have doubts.
For an 8’ high drop (by any length) I always go with dye sub fabrics. They give you the most vibrant color punch and there is a slight, a very slight, dot gain to the process that helps with images going large. The other thing is, the dye sub doesn’t reflect stage lighting like a vinyl might.
An 8’ drop isn’t all that large. Is it 8’x8’ or 8’ x 60’? That’ll make a difference in the image you need to acquire.
Here’s the other thing about scenery. If people in the audience are focused on the backdrop, what does that say about the content of the show? While you want the best imagery possible, remember not to upstage what is meant to be the focal presentation of the event.
As with all imagery though, the GIGO rule applies.
Garbage In, Garbage Out.
Get a proof.