these photos have the highest resolution of the lot, with the long edge between 5000-8000px. many of these can print at 60" wide.
these photos have high resolutions, with the long edge dimension around 4000px. many of these can print at 40" in the long dimension, but they may not be extremely sharp. the cannon beach image has nearly a 5000px long edge in this uncropped version, but its height is only 3264px.
these photos have medium resolutions, with the long edge typically less than 4000px. this doesn't mean they can't print at 40", but you definitely want to run a test strip first.
many of the photos can be cropped to to a new aspect ratio. 4x3, 3x2, 7x5 are going to be available for most landscape oriented images. 4x5 and 5x7 for portrait oriented images. some images can't have a new aspect ratio other than what you see. we can cross this bridge once final selects are made.
some subjects and photo treatments allow us to get away with printing a smaller file at large scale. for example, if it's a foggy scene, sharpness won't be much of a consideration. likewise, if there is heavy grain, that also allows the viewer not to care so much care about sharp details. while printing large, sharpness isn't always as important as we first think.
the porsche image is a good example of what can likely print bigger than its technical limitations.
viewing distance: if a photo is hanging above a counter or above a sofa, that means it's going to keep people a couple feet at bay (or thereabouts) at all times. and it isn't always physical limitations that prescribe viewing distance. some photos make people want to step back and take it all in, enlarging the viewing distance. others draw people in.
the best advice for every instance is to print a test strip at the desired resolution. this is to check resolution, darkness, and color. if this isn't doable, then we can rely on image resolution, comparing to a print chart that suggests minimum ppi for different scale prints for sizing. and i can estimate how light to make the image before releasing to printers.
printing on uncoated paper produces the best results, in my opinion.