Mathews at least in 07 was using 452x. They were using a lower strand count as well, lower than what BCY recommends.

I waited until I personally shot the bow today to post anything to prevent spreading misinformation. I shot the bowusing a 325 arrow, cranked down to 65lbs. Keep in mind you lose efficiency typically when not shooting a bow at peak weight. The bow had a peep, loop, and nock points tied in, and was using a NAP Quicktune 360. At 29" (measured actually 29 1/16" AMO) it shot 322. This was produced through the same chrono that gave me the speed I used for the sight tape for my Constitution. That sight tape is accurate to 80 yards, so iI would say that chrono is pretty dead nuts.

The bows draw weight was measured on a Pelouze 7710, most likely the most accurate commonly available hanging digital scale. Based on what I saw,I'd say their speed rating is pretty darn close.

I rarely believe when most people share speed #'s online, it's too easy to use a bow scale, chrono, or arrow scale that will produce poor results. Just MHO, but there is no way to ensure consistent measurements are being made.