For some emphasis/maths on OA2-4 sword:
3QA/11TA/29DA
100 * .03 = 3
3 * 3 = 9
109 attacks/round
97 * .11 = 10.67
10.67 * 2 = 21.34
130.34 attacks/round
86 * .34 = 24.94
155.28
1.5528 attacks/round
KHADGA (40/30/20/10 distribution)
100 * .10 = 10
10 * 3 = 30
130 attacks/round
90 * .20 = 18
18 * 2 = 36
166 attacks/round
70 * .30 = 21
187 attacks/round
1.87 attacks/round
However this isn't accounting for the fact that Khadga does not have individual multiattack procs like QA/TA/DA, the final average hits/round is about 1.9~2.
So how does your natural multiattack affect you?
0.97 * 0.89 * 0.71 = .612943, or a 61.2943% chance of not getting a multiattack proc from QA/TA/DA, 38.7057% chance of getting a QA/TA/DA. This means that you have a 38.7057% reduction in bonus attacks from Khadga, which means an average attacks/round for your offhand of 1.387057 + normal QA/TA/DA.
Average attacks = 1.612943
(1.5528 + 1.5528 + 0.612943)/2 = 1.8592715 attacks/round avg
So, a 19.7367% increase in attacks. That's actually well under my previous estimation of a 50% increase in TP gain. When factoring in delay, which is about a 3~5% reduction in TP/s, you're looking at a very poor option.
@Laffter, I'll add augments.