This is the thing. Legendary Speed 1 modules can be quite effective because they don't provide as much of a bonus or penalty. For fewer module machines, like crushers or chemplants, you may want to even add an empty/eff beacon just to dial it back even further. For cryos, because it's 8 quality modules, you get some grace on both numbers. The speed bonus will mean more, going from -40% speed to +272% speed from the speed 3 module is a 620% speed gain, because of how bad the speed penalty was to begin with. The quality penalty will also mean less when compared to a machine with fewer quality modules, taking 6% away from ~50% is about a 12% penalty, whereas taking 6% away from 25% is a 24% total penalty, dropping it to 19.
10% of 1,000 items/sec is significantly larger than 25% of 100 items/sec. "Oh but 900 waste" Yes but you see, those are second order chances. You recycle them and get another chance to roll higher quality materials. Particularly with something like electric engines, generating more low quality engines allows you to roll more dice at the second order, and then the ones that fail again get to be third order.
The numbers are usually not so extreme in game, that's just to show clear examples. The plastic one is just the most cut and dry because it's purple plastic; If the quality goes up, it's going up to legendary. .371* 178 is 66 legendary plastic a second. .434*96.7 is just shy of 42. .496*15.6 is 7.74.
Second order chances on the remaining 112 purple plastic is *0.25 *0.248(no need for speed on this step but you could) is 6.94, third order is 1.31, so that's an additional 8.25 or so, just over 72 legendary plastic per second. Just the second and third order chances on the speed beacon version generates more plastic than the one without any speed.
Obviously if you can't keep a machine supplied, don't speed it. Particularly higher quality products, those can have pretty serious impacts. Stuff with prod techs are also obvious candidates. This is one of the better ways I've found to generate legendary iron on nauvis so far
It takes like 3 miners of each so like... yeah that's relatively compact for what it yields, compared to most of the other stuff I checked that's going straight to legendary. The beacon on that build straight up halves the size. And it's 100% efficient for materials b/c it's recycling blue chips so like... it doesn't even matter if the chances are lower. Just roll the dice again.