Originally posted by pjtn 40"is a very large print from a non stitched file. I only print to 16x24", surely the K5 would perform tremendously in this circumstance. I really do wonder if a difference would be visible.
I'm not a fanboy, and before you changed lens choices, I suggested the Canon, because I thought you had better landscape lens choices with it. For enlargements, it's not just the megapixels. Much of it depends upon how well the lens records detail. With the 15mm and 31mm, I'm now firmly in the Pentax camp.
I do quite a few large prints. My K20D does "tremendously" at 20X30, and the K5 has a couple million more pixels. I even had an outfitter once enlarge a JPEG from my K20D to a 4-foot by 8-foot banner and surprised me with it. I was amazed at how well it held up and it looked fine from a dozen feet, although suffered close up. I can't tell any difference in 8X10 prints from my 14.6 MP and 10 MP cameras. In other words, the K5 will give you more than enough for 16X24. In fact, I think both the K5 and 5D are overkill, given equally good lenses.
Everyone argues body models (which the manufacturers love and encourage), but I've learned from decades that the glass is where it's at. The body gets you there, but it is the eye (lens) that sees.
I'm also quite confident you will be pleased with either system, but for your purposes, I think you will be happier with Pentax (15 and 31). If you were shooting products, I'd reverse that, but for landscapes, Pentax produces richer colors (past models), and as far as I can tell, the K5 retains that at low ISOs. The lenses give you the detail and contrast.