I'd stick with the 6x6 and crop down to 6x4.5 only if you feel the need. Not sure if the VF in your Yashica has crop lines or not for 6x4.5 but that helps also. Personally I love the 6x6 format. But I also have a 6x4.5 camera. I don't think I'd like to be stuck in one format or the other but there are many that do. Basically you will find out if you like the square format by shooting your Yashica and studying your results. You may find yourself cropping to 6x4.5 (rectangle), and if you are cropping alot, maybe you prefer a rectangular image better than square and then could maybe pursue a 6x4.5 camera like the Mamiya or even a 6x7 camera.