Edit: the value of Ac is correct for the rating on gear, i was looking at rating in character pane, which reflects the passive 5% increase to rating. Values below have been updated to reflect this.
I'll try to explain what he's doing. It makes a little more sense if you convert the percents to stat ratings (using the values from the 2nd post).
Code:
Mastery Crit Mt V
-166 (0.104) 1198 234 -1766
-97 (0.114) 1256 207 -1793
-28 (0.124) 1314 181 -1819
41 (0.134) 1372 156 -1844
110 (0.144) 1429 132 -1868
179 (0.154) 1486 110 -1890
248 (0.164) 1542 88 -1912
317 (0.174) 1599 68 -1932
386 (0.184) 1655 48 -1952
455 (0.194) 1711 30 -1970
524 (0.204) 1767 13 -1987
593 (0.214) 1822 -4 -2004
662 (0.224) 1877 -19 -2019
731 (0.234) 1932 -34 -2034
800 (0.244) 1987 -48 -2048
869 (0.254) 2041 -60 -2060
938 (0.264) 2096 -72 -2072
1007 (0.274) 2150 -83 -2083
1076 (0.284) 2204 -94 -2094
1145 (0.294) 2257 -103 -2103
I put in the mastery effect in parenthesis so you can compare to Havoc12's chart.
The first lines are a negative mastery rating because we have 12.8% base mastery.
What he's looking at is, for a given amount of Mastery rating, what rating of stat 'X' do we need where an increase of 1 rating to either stat gives the same throughput increase. So, at a given line in the chart, if you had the ratings shown, an increase/decrease of any of the stats should have the same effect on your throughput (of non-absorb spells, ie excluding PWShield and CoW). A negative rating means, effectively, you should be avoiding that stat, not that the stat itself is harmful, but you just don't get enough out of it.
There are a couple of things to notice here. The first is, even with around 0 mastery on gear, you need a decently large amount of crit before adding any mastery is better than adding more crit. The second is, multistrike should be better than mastery (for non-absorb spells) up to a decent amount of crit (about 1400). Here's the chart based around 0 mastery on gear:
Code:
Mastery Crit Mt V
-345 (0.078) 1046 311 -1689
-276 (0.088) 1104 280 -1720
-207 (0.098) 1163 251 -1749
-138 (0.108) 1221 223 -1777
-69 (0.118) 1279 196 -1804
0 (0.128) 1337 171 -1829
69 (0.138) 1394 146 -1854
138 (0.148) 1452 123 -1877
207 (0.158) 1508 101 -1899
276 (0.168) 1565 80 -1920
345 (0.178) 1621 60 -1940
414 (0.188) 1678 41 -1959
483 (0.198) 1733 23 -1977
552 (0.208) 1789 6 -1994
Hopefully this makes it a little bit more clear what's happening here.
Remember that PW: Shield and CoW will scale better with Mastery than Holy Nova/Atonement/T90, so depending on your anticipated spell usage, it may be better to avoid the multistrike for mastery even early on.
Edit 2: fubar'd the baseline 5% crit chance.