Both are shitty/ difficult rates.
your best chance might to wait to have HBR quest with a decent amount of Ill Gills.
PW4 and Lost Charge Vulcan are on the HBR list, with full team bonus it reduces the odds under 1/10000.
Girtablulus DAR is already 80 % so the regular weekly boost will already bring their DAR to 100% (1/6553 ) Xmas fiasco might be one of the most efficient way to hunt them.
No particular need for HBR in that case.
Lost Spirit Striker also have a lot of those giant crabs but the quest takes more than one hour.