It's not a grain issue, because I don't even notice the grain. It's more a loss of definition that bothers me with the larger prints. Taking pics of my dog and family, like I've posted above, is great with the 35mm setup I've got. But, my real interest lies in landscape photography, and getting pics that I can enlarge to 20x24 or so to frame and hang on my walls. I am a fan of Clyde Butcher, have been to his gallery (I used to live in South Florida) and have a few of his prints in my home. Seeing his work made me fall in love with photography more than ever. Now that I can develop my own prints, I am hoping to travel and get some of my own that I would be proud of, with a similar look (though I don't expect them to be in that league, but the closer the better). Since I now can see that would be impossible to achieve in a 35mm format, I made the leap to MF. I know Large Format is not for me... not in my budget, won't fit in my car, and I wouldn't be able to carry it around. So, I am hoping to be able to learn to use the Mamiya well enough to get the type of prints I want.
My camera hasn't arrived yet, but I've been reading the manual, and I realize it's going to be a lot different. I will hold off on asking questions until I get it in my hands and start using it... but I'm sure I'll have many soon.