I've decided to revisit big cassettes while running GRX400 2x 46:30t 10spd. I originally was running a heavy Deore 11-42t with GoatLink, but I felt the weight and shifting performance wasn't worth the low gearing and went back to an in-spec 11-36t cassette. Fast forward this week and I finally came across a now rare Sunrace 11-40t 10 speed cassette CSMX3 in black (the color I wanted). I ordered it and just installed it. I had to use a Goatlink to make it work, but so far shifts seem crisp and the gaps between gears are well spaced. Also it clears big/big just in case I accidentally shift there which I hopefully don't! Weight-wise it actually felt either the same or slightly lighter than my all steel Shimano 11-36t HG-50 cassette I was using. Looking at listed weight specs, they are only within a few grams of each other.
Doing the math, my low gear ratio of .75 is about the same as a 1x with a 38t + 11-51t or a 42t + 11:56t, while still having the high gear of 46:11t in the big ring!
