Without Offhand Precision on average 8% of my damage is from offhand attacks at 86% offhand. With it at 96% 8% of my damage is still from offhand attacks. No change.
My spec is: http://goo.gl/bpv5M Full T4 minus rings and cloak.
Yes, I have spent countless hours testing multiple builds focused on specific feats and this is the purest dps build I have come up with. It does not always make sense just looking at it. Feel free to try it out and give me any feedback. I check the forums every six months or so. For those curious the build parses just short of 2k on a strawman and has hit 2400 in raids.
So, what the person was trying to say was it has diminishing returns, which is correct it does. at 86% I had 121 hits in a five minute parse. Then with 96% offhand I had 138 hits in a five minute parse. Over five minutes I do not believe 17 more hits with max being 784, median of 310, and min of 176 being worth five feat points. At 86% I had an offhand hit proc'd on average ever 2.5 (rounded off)seconds and with 96% it proc'd ever 2.2 seconds. This not a 10% increase by any means. Feel free to test it yourself. Again, given the tooltip says "X% chance of offhand strike." It is not a given that it will happen 10% of the time. I would still rather have 42.5% weapon damage that affects every attack, than 10% chance at an offhand strike.
Now, I have not run tests without Improved Discipline as of yet. Raw weapon % cannot be beat when it comes to feats so I have always taken it if I can. Might test this out one day though, maybe.