I've been looking to replace my park board(2011 Rome Artifact Rocker 150). I wanted a board with a R/F/R profile in 151-153cm range. I weight ~160LBS.
I've demoed Ride Machete and K2 WWW in 152. If you check the manufacturer weight recommendations for each board I'm out of range for the Machete(100-150LBS) and right in the middle for the WWW(120-200LBS).
Yet the Machete felt noticeably more stable and was much harder to press and butter than the WWW. Machete felt more stable on jumps and just trying to go fast.
So how accurate are some of the manufacturer's weight recommendations?
Well these are two very different boards so right off the bat you're comparing apples to cinderblocks -- these boards *should* feel different to you, no matter what size you're riding.
On to the topic of weight ranges, though... These "weight ranges" are basically designed to appeal to the broadest possible customer base
IMO, at best the weight range is basically a starting point suggestion, and in most cases it is such a broad range and with so much overlap between sizes that it is nearly meaningless. To use one example, the weight range on Arbor's snowboards typically span 70-80 pounds per size, and each size increments only by only a few pounds over the previous size. Here's a specific, go look at the spec sheet on the Coda Camber:
Length | Weight Range | Average Weight
154 | 114-194 | 154
156 | 120-200 | 160
159 | 126-206 | 166
161 | 130-210 | 170
164 | 132-212+ | 172
So, as long as you weigh over 130#, Arbor says you can ride *any* of these sizes, but it should be pretty clear which size(s) are most likely suitable for someone of that weight. And likewise, as long as you weigh under 194#, Arbor says you can ride *any* of these sizes, but it should be pretty clear which size(s) are most suitable for someone that size, too. When you look at it in this full context, it's kinda ridiculous innit?
Just understand that the heavier you are, the more flex you'll tend to get out of the board, stiffer boards will not be as stiff, but softer boards will be even softer, and factor that in to your decision as best you can.