Is it the biggest contributor to a decks sound? Looking at the ultra versus studio they seem pretty close except for the carts.
No, the cart is not the only difference between the two. The Ultra has a heavier platter, a better bearing, actually uses a sapphire thrust pad, similar to what is used in my SOTA Sapphire, thus it’s name, the Ultra uses a layer of aluminum in its plinth vs only MDF, the Ultra has Cardas wiring in the arm, the arm on the Ultra is also internally dampened and the bearings used are better. So no, there are other differences between the two, not just the carts used. I was strongly considering the Ultra before going the SOTA route with separate arm and cartridge.
Be careful not to ‘chase’ something you think you are missing just by swapping carts. I’m certainly not saying the Cearaudio may not be an Improvement, it may be, it should be. If you can get it for $400, that is a good deal, but how many hours does it have on it? That isn’t a stylus you can replace yourself.
I guess the question should be; what are you trying to improve? What do you think is lacking? And most importantly; what are you trying to make it sound like? Are you comparing it to something else?