You're right, I didn't scroll down far enough. I only saw the higher illustration showing 10ft clear spans. It looks like that style, with four 4x4s under the joists, is really popular today. Every shed around that size I've ever built or owned or rented has had 2x6 or 2x8 for the 10ft span floor joists, without a center support, but they were all built 20+ years ago.