Data is not the plural of anecdote. Your testing against a solo mob has very little to do with the results you should expect in a raid.
I recently got the Stakethrower and hit 2T10 - so I started fiddling with the Spreadsheet wether to got for 4 T10.
Couple of things seemed odd to me, so I did some 3 hours of testing against the heroic Dummy.
1. I had to do at least testruns of 15 minutes to get enough data to be somewhat reproduceable at all.
2. Hit is by far the most devastating stat below the cap (a no brainer, but made me trust my collected data =) )
1. Arcane Shot / Steady Shot don't seem to be modeled properly:
According to the Spreadsheet (applied to The World of Warcraft Armory - Soriaya @ Malygos - Profile) Steady Shot should be 300dps better then Arcane Shot (recommending to drop it), but my collected data give Arcane shot an 600 to 800 dps advantage over Steady Shot, even when not specced. So do I miss something her?
2. 4T10 is calculated far worse then 2T10 + 2T9, can that be?
3. Gemming for ArP costs me aprox 5 dps per dropped Agi gem, even with full T10.
So you find me a bit uncomfortable with the spreadsheed....