Deducting 1 point from Presicion leaves you undercap by 10 points which you can easily cover with 10agi/hit gem. Now heres the math
You have to gem 10hit which means you gonna lose 10agi or crit for it. If you choose to lose agi it will be even less than 10 agi due you can get a yellow socket bonus lets say 4 agi. So 6 > 7 agi you lose.
7agi=7atkpower
But +1 talent to spent on.
+1 Imp. Hunter's Mark = 50atkpower bonus if you mark by yourself which proves gain directly, but on other hand, if you are using range talent, you can get back 1 point at Imp. Barrage aswell.
The VDW 25hc ring is the BiS one. If you're a Hunter in t10 gear you have no business touching the RS ring for the most part.
Also Focused Aim brings more value than just the Hit. Not being pushback immune on Steady Shot is going to end up being a noticeable loss on one fight or another.
Even with 3/3 Presicion, Twilight is better still from Frostbrood. With Frostbrood you need 30 hit from gems (30 cause putting lower gem like +5agi/+5hit or something will makes you loose more stat.) and when you get Twilight ring you get +17 more from Frostbrood yet you get more stats from ilvl (more crit/agi/atkpower.). Lets compare:
If I didnt do anything uncorrect this is the result
Twilight has 13atkpower more and %0.02Crit(1 20crit gem=%0.44Crit) more, but this is without its gem.
Lets say we gem it 20agi and 10agi/10crit respectfully
20Agi:
20 x1.144 -> 22.8 -> 22(Due flooring.) agi
22atk x 1.1 -> 24
%0.26Crit
=+35 Atkpower + %0.28Crit more from Frostbrood.
10Agi/Crit:
10 +4(Socket bonus.) -> 14 x 1.144 -> 16
16atk x 1.1 -> 17
10Crit -> %0.22 +%0.19(From agi) -> %0.41Crit
=+31Atk + %0.43Crit more (both combined is equal a bit more than a gem.)
If I didnt calculated somewhere wrong, its clear with any kind of gem Twilight is BiS without question.
They are different 30s cause I also added 38 as ArP bonus to Frostbrood
With frostbrood you have 68ArP which means 68Agi directly but you lack 30hit aswell
And with Twilight Signet you have 57hit but overcap by 22, so not fully effective converting to agility. I deduct the difference with Frostbrood endhit rating. So only 30hit is effective from Twilight. Sorry If I made things a bit confusing.
Here is what I typed:
57Hit -22+5
-22 is overcap reduct and +5 is to make it equal with Frostbrood since it also has +5 overcap hit when you gem it.
Signet:
109 Agi
145 AP
73 Crit
34 Hit (57 Hit Rating on the ring, but we know that 23 points are wasted).
VS
Frostbrood:
102 Agi
120 AP
68 Arp (None of which is wasted if you gem smart)
60 Crit
After having cancelled out the common stats between both rings, the comparison comes down to:
7 Agi
25 AP
34 Hit
13 Crit
VS
68 Arp
Converting the AP into a commensurate amount of Agi, as per MM stat weights, 25 AP can be generously regarded as around 12 Agi worth of stats. Viewing the Hit rating on Signet as Crit - because that's what you'd have more of if you didn't have to gem Hit, and likewise viewing the Arp on Frostbrood as Agi, as that's what you get more of from saving the need to gem Arp, the overall comparison further condenses to:
19 Agi + 47 Crit (Signet) vs 68 Agi (Frostbrood)
Now again, cancelling out the common stats, we simplify this to:
47 Crit (Signet) vs 49 Agi (Frostbrood).
49 Agi has a good edge over 47 crit not only because Agi is more valuable, but also because there's slightly more of it. This all disregards the the socket bonuses which slightly favour Frostbrood anyway.
Its not ArP goes waste, but since you gonna need 30hit from gems solid you cant gem 30agi (You might wont need hit due gear but it also means nothing is lost from Twilight aswell but BiS gear its like this, Twilight +23 (which is 17 since Frostbrood after gemming hit has +6overcap) and Frostbrood -30. And I dont think gemming crit instead of agi would be better since agi scales with buffs, maxi you could 10agi/crit on some slots.
PS: More is more, I calculated with buffs on due every +10 is 11 or more in raids.
PS2: I made an error as I see, counted 30agi from twilight yet it is 40 which makes it a bit better more.
Its not ArP goes waste, but since you gonna need 30hit from gems solid you cant gem 30agi.
If you gem smart the 30 hit will come from 30 Crit rather than 30 Agi anyway.
You should be going 10 Agi 10 Crit in every yellow socket anyway, unless it's tied to a blue socket which you don't intend to pick up with a Nightmare Tear or with the 10 Arp 15 stam gem. 3 of these 10 Agi 10 Crit gems becomes 10 Agi 10 Hit gems. If you're a JC you can use a +34 Hit yellow gem to cap the hit off perfectly at 164.
What you say is true but when you gem 10agi/10crit you already sacrificing 10agi for crit so its the same. I think you should add -30crit to last calculation this way.
If you gemmed 10 Agi 10 Crit, it would be to secure an overall gain by satisfying socket bonuses somewhere, thus it would not be a sacrifice at all as in that situation, the 10 Crit is a better option than 10 Agi.
I like to get socket bonuses when chance rises but still with Frostbrood whatever you do, you need to gem those 30hit, therefore gonna lose either agility or crit. 34 hit gem would be optimal due to not overcap but still you could be gemming 34agi or crit if you didnt need that.