For the last 6 years, I have been placing 4’ wide bales spaced about 1&1/2-2’ apart on the bottom, and the double upper row bales butted tight side by side so there’s less chance of falling off. I only had a few of the many many hundreds of bale loads get tippy when I load and transport this way.
Were I you I would be more worried about the transport width of 2 5’ wide bales than I would be about any other facet of making 5’ bales. And I would spend exactly 0 time looking for a 5x5 baler. Go 5x6, lots more to pick from.
If I did 5’x 5’ bales and butt the bottom double row tightly together, it’s the same width, but now the upper row is just a single row in the middle, which won’t be nearly as tippy as a double upper row.
So why would transport be a “worry”, when it’s less top heavy and less tippy?
In the picture, the bales are overhanging 8-12” over the edge of a 102” wide trailer. (The back pair is butted because the mega ramps are only 96” wide).
If they were 5x5’s they’d overhang only 6-8” on a 102 wide trailer. So I can go down the road at a little narrower width, too.
While I do agree a 5x6 baler is a more versatile choice with greater selection, the 1500 extra pounds shoving me down steep hills is a safety consideration and the pulling a 5x6 up a hill with a 1100lb bale is going to require dropping a gear or 2 compared to a 4x5 baler I currently use. A 5x5 baler is lighter than a 5x6.