WT: that's interesting. Not a slur on you OR the magazine, but most test data I've seen has clocked the Winchesters faster. Nyclad 158+P are more commonly at the low 800s, sometimes high 700s so that's within normal bounds (talking about 2" barrels only). It's the Winchester numbers that are unusually low compared to other tests.
Could have been an off batch, could have been a gun that just didn't like that round. It happens. In fact, take another look at the numbers; the same Winchester load is faster in the 6" barrel, which suggests it just wasn't compatible with whatever gun they used with a shorter tube.
(Picture how the magazine tests: they've got three guns, one of each tube length, each one shoots both types of rounds. Good so far. But one gun is incompatible with one type of round, another one doesn't like another. Hence numbers like what we're seeing.)
Remington's version consistently clocks the highest, often up around 875ish from a 2", not less than 850 of the various reports I've seen. (Well, "highest" until that Bufallo Bore load finally ships!)