(idk where ppl got 5~6)
head: 2 haste, hands: 3-4 haste
really, with haste rounding it should be ~5 assuming you have the gear (which you've already told us before you don't because you're a deceptive tool) to hit "actual" (~26% "written" haste) haste cap (see: 6% haste belt which is ~30-40m by itself, etc).
SC dmg, COR, blahblah
You could just get BRD+RDM+DNC(instead of COR) and SC more w/ 6hit on top of higher melee DPS (from higher acc/atk/STR/speed) and WS dmg...
5-hit w/ COR: 7.5*4*.34 = 10.2 sec/WS (sacrificing haste as above)
5-hit w/ COR: 7.5*4*.30 = 9.0 sec/WS (same gear haste as 6-hit)
6-hit w/ DNC: 7.5*5*.20 = 7.5 sec/WS (magic)
SC dmg is also generally resisted vs higher level stuff, meaning you would built an entire build around 5-hit GK SC, in a level/buff range where you could make a ridiculous polearm build if you put in the same effort instead.