What length midi cables between mc8 and strymon big boxes?

and in between the big box strymons? Is the 30 cm what most of you use?

Really depends on your board/layout. Are they right next to the controller? Are you routing under the board or straight shot on top? You can lay everything out if you have it already and use a piece of rope or string to get an idea how long of a cable you need. I’d add a little to accommodate plugging in.

Right beside each other (they would be daisy chained, no?). Just wondering if others have used them.

Personally, I’d use the shortest I could find. Additional length in any cabling can often lead to issues. There are extenuating circumstances but shorter and tidier usually means better and more stable.

IIRC in the MIDI specifications, there a maximum length recommended for MIDI Cables and its like 26 feet or 26 meters or something.

but yes, using the shortest required would keep everything neat(er) but using a longer length shouldn’t do any harm.