I don't know how long is an inch

....
Anyway, I know that if you partecipate in the
Renderosity contest for the magazine, they ask for a TIFF format 300 dpi depth...
I think you can ask the size you want for your pictures, obviously if the size you want is 8x10 and the picture is not exactly in the 8:10 ratio you will have 2 sides with a larger blank part. I saw your pictures are larger than 8x10, so you can't loose resolution.
I'm printing some of my pictures for the wall of my house

in standard A4 format (21x28), I lost a little resolution if the original was smaller , but it is enough for me...