Ahh, good thread.
I'm now used to sub 8ft Sup surf boards in waves, I prefer smaller waist high than larger over head stuff.. but that's by the by. The point I'm making is I'm happy on small boards, my little Shroom is 7'9x30" and that's a great little toy.
But the other day I borrowed a 14'x24" race board for our "round the island" race..14miles of it.. and I thought to myself I'd be fine on the race board, that I wouldn't notice any difference apart from length..
How wrong was I.
I tripped up, fell over, wobbled and generally looked like a total beginner

Until I got some speed on, then it all came together.
Never again, 14miles is a long way