To your question... will any aperture over 50mm F10 matter? Yes. While there is vignetting going on, it's not harming resolution, it's harming the illuminated circle on the sensor, which is actually fine, because the entire etalon doesn't produce an on-band image anyways, so smaller than the etalon is what is more likely useful, on band.
For example, here's 120mm F10 with PST etalon (no GPC, just an aperture mask). A 50mm aperture cannot resolve spicules on the surface to this degree. So again, while there is vignetting, it's ok, but it's not reducing resolution. You're just imaging a portion of the total image circle, but a lot of the edges through the outter edges of the etalon are not on band anyways, most PST mods are ideal for high res with small sensors imaging through the sweet spot.
Your 150mm is going to have resolution of a 150mm, if seeing allows you to resolve to the limits of your aperture. Again, just a little vignetting reducing the image circle on your sensor potentially, but again, your imaging a portion of the light cone, at the full resolution of that area, in the sweet spot, that is on band.