I have tried both drivers in another shell from Huayunxin, wind chime, and as far as i know both it and the one you want to pick are to the same or very similar internally.
Personally, i don't think this shell matches very well with any of these drivers, 400 ohms graphene likes lots of air, and the air flow in this shell will not cut it.
As for 300 ohms blue pet, they're more versatile in my opinion, they operate well with moderate or restricted air flow, and should work in this shell, though, i didn't liked how they sounded in wind chime, the midbass was too loose and treble wasn't elevated (as for my preference).
Later when using wind chime with 120 LCP i discovered this shell lips tends not to seal well with the driver, so you have to put something in it to make it seal, or glue it, so this may have affected the results.
Both 300 ohm blue pet and 400 graphene are among my favorites, and i think they are incredible drivers, but not in this very especific shell.
I will add that, i from some photos on Huayunxin newest driver, it seems they tuned their drivers to be used with their shell, so it should sound good togheter. Don't know if it does apply to their other drivers though. And that driver is very expensive also.