Not that I particularly like this GKT, but I'd like to point out that the whole point of X-hit builds is to get to a lower amount of time between weaponskills.
E.g. for a 6 hit build with a 450 delay weapon, you're looking at WS + 5x 450 delay before you WS again, or 2250 delay. For a 378 delay weapon w/ a 7 hit build (1 more storeTP), you're looking at WS + 6x 378, or 2268 delay. So, the difference in delay is pretty minimal. As was already pointed out, the lower damage weapon will hurt your WS damage quite a bit, so the higher delay/higher damage gtks are better.
you'll also get a greater increase in WS frequency going from 6 to 5 swings to WS than going from 8 to 7. this is, in part, why 1handers don't make X-hit builds.
re: "swinging GK" above, soboro vs hacchowhatever:
soboro: 50*2 = 100
haccho: 80 * 1.2 * 1.025 = 98.4
those numbers being weapon damage + fSTR * DA rate for soboro, and WD+fSTR * speed advantage * inherent DA effect for haccho. DoT will be around even, while soboro will WS a significant amount more, or generate more /DNC TP, or whatever.