well, I have (well my wife has) a garden that is about 100' by 50', give or take, but I till all my neeighbours gardens too, so I do about an acre a year. I have a 48" tiller and it works fine.
Many tillers 'side shift' to they don't have to be big to do the job. I said it a dozen times before, but tilling is so fast and efficient with a CUT and tiller, you don't have to go for size.
ps: if you have a garage with a solid floor, make a dolly to move the tiller around with. It really speeds up attachment.