If you don't want to use a prism on 645 you have to take all your shots in the landscape format,which is a pain, one of the beauties of 6x6 is that it can be cropped in either vertical or horizontal format without doing acrobatics with the camera.Since you are new to medium format and are pleased with the results you are getting with the 124 G I would stick to what you have for now and if you want to upgrade in the future think about a medium format camera that will accept interchangeable lenses to improve your versatility like a Mamiya C330F or a Zenza Bronica SQ SLR.