What's "RM750x Gray" ? There are RM-x 2015, 2018 and 2021, all with basically the same label color aside for 2021 version which is easily distinguishable by the new casing design. And then there's old RM from 2013 with yellow accent on the label, RM from 2019 with gray (more like black actually) label, and the 'new' RM 2021, basically the only difference of which over RM 2019 is the new casing design similar to RM-x 2021. RM 2019\2021 are technically inferior to RM-x 2018\2021 because of cheaper capacitors if that what's you're asking about. But Corsair still offers 10y warranty on it so it hardly matters.
PS: It's me or everything is bold here for some reason ?