What I like to print and what customers want are sometimes two different things. Customers in many of our targeted demographics have larger and larger homes, thus the desire for large prints. As an artist, I find myself working on smaller prints in the 14x9 range from my 5d.
I recently viewed the "Perspectives on Change" photographic exhibit sponsored by A.G. Edwards. The exhibit features prints from Weston, Lange, Sudek, Steiglitz, Steichen, Eastman, Arentz, and many others. Palladium, dye transfer, and silver were the materials.
For me, the most powerful print was by Sudek of a glass of water and a flower in it. It was probably 8x10 at most. Steiglitz famous "Spring Shower" was equally powerful and was merely something on the order of 3x8 at the most. The largest print was an Eastman color print, maybe 30x40, and artistically it made no impact on me at all. The significant majority of prints were 8x10 and 11x14 roughly.
So, the short answer for me is that artistically, I prefer a smaller print in line with a straight 300dpi conversion from my 5D giving a 14x9 print. This gives me outstanding quality and is a very clean translation from visualization to print. But from a marketing standpoint, larger prints are certainly in demand from our targeted high income/large home customers.
So, until my artistic reputation exceeds my need to satisfy customer wants for large prints, I am printing as large as the customers requests. That is as long as the quality holds up, which for my 4x5 transparencies is quite large. But in the long run, my artistic desire is for my prints to have an emotional impact in a modest size print on the order of 14x9.
Good luck in your decision making process on print, matting, and frame sizes.