Sorry for being less than clear...
I had two images taken with two cameras, Sony Alpha 700 and Sony Alpha 900. Same image, tripod, MLU, different lenses. I than scaled up the image from the Alpha 700 12.5 MP to the same size as the image from the Alpha 900. The image from the Alpha 900 was much better, as expected. This was just for comparison.
I than printed the original (unscaled and unmanipulated images) from Lightroom with normal output sharpening at a resolution of 480 PPI. I don't recall the setting on my Epson, but it was probably 1440 DPI, possibly higher. To my surprise I couldn't see any difference. I also asked two collegeaues about their opninion, one having considerable experience from a professional photo lab. They could not see any difference either. The crops I had corresponded to about A2. The subject I photographed was a mural painting with good detail, but probably not a lot of very high contrast and high frequency detail.
As the difference in print from the two files was so small I figured that output sharpening in Lightroom may have played a role. In my eyes both prints were absolutely good enough.
Also, thank you for taking time to answer my question!
That would have an impact for sure...unless you are at 1440 minimum and ideally 2880, you might not see much printed difference unless you are looking at super high frequency and/or high contrast diagonals.
You could recreate the test and simply output as a JPEF two images...on at native res and one at upsampled res and visually compare the resulting images...you could then output both images from Photoshop to confirm there would be differences...
As to the A900 vs A700, not sure what you are referring to...do you mean you did the exact same shot with an A900 and an A700 and tried to upsample the smaller capture to the same size as the large capture? Then what did you do to the image? The process you are talking about is unclear to me...