I wear size 9 snowboard boots and am around 170 lbs. Have over 200 days on my TRice 157 which has a 25.8 waist and no problems what so ever with anything. Started riding a 156 Niche (basically the same board as the Trice except lighter and snappier) this year and that's a 25.8 waist also. Still nothing but fun.
That said, I would not go wider than that, 25.8, which is considered a mid-wide for a 156,157 board.
Try this trick and spin it, yeah
Your head will collapse