Use both in PvE. Deadly strike can double your Crit DMG and with Brutal mythic, 3x Crit DMG. Crushing blow can help reduce enemies HP in higher floors to finish them off easier. 350% cap crit dmg , deadly strike will mean 700% crit dmg. Well there is a hidden 50% crit dmg so its actually 400% crit dmg or 800% when deadly strike is done. With brutal, its 1050% crit DMG aka 350*3 (350% is still the crit cap but it is x3 when deadly strike happened) or really its 400%*3=1200% but you get the idea. Deadly strike can easily double your damage output and crits already increase dmg output by almost 4x when capped (or almost 50% or more without any crit dmg affix).