(If this belongs in the Feral Druid DPS thread, please merge. Posting separately because of the difficulty I've had trying to follow specific theory discussions in the mixed advice/theorycraft mega-threads, but it might be just me.)
It's pretty well established that one of the best uses of item budget in PVE for rogues and cats is Hit Rating, at least up til the point where special attacks aren't missing (currently thought to be 8.6% vs bosses).
I'm working on a yet-another feral spreadsheet and the first cut showed 1 hit rating valued at 0.95AP. The gear set I used wasn't hit capped (according to the model I used) and all the other stats appeared about right. I couldn't find any obvious bug and back-of-the-envelope calculations seemed to confirm it. Either something's wrong with my assumptions, or my model, or +hit is much worse than I thought. Here's my rough calculation.
Assumptions- I'm going to treat dodges/parries as misses, as the mechanics don't seem to differ for our purposes. Dodges/parries can't be removed by +hit of course, but I'm looking at the marginal value of hit when not hit-capped, so this doesn't matter.
- I'm going to ignore cooldowns on abilities and assume you're limited by energy rather than cooldowns. If you're missing so much that your energy bar fills up faster than you can use it, your DPS is going to suck, but this doesn't happen. More realistically, if a druid misses a mangle then it messes up their cycle. (A naive approximation of this effect - reducing mangle-uptime-on-rip by an additional 0.35% per %hit increased Hit Rating's worth to 1.13AP)
White damage
White damage is simple, it crits, hits, glances, or misses. Hit rating converts misses into hits.
Your average swing is weapondmg * (2*critrate + hitrate + g * glancerate). I'm not sure on the coefficient for glances but let's say 0.8. With 30% crit, 15% glance, 55% hit, 10% miss/dodge/parry, this is weapondmg * 1.27.
If your weapon damage is X, then 1%hit increases your average swing by 0.01X, which is 0.8% of your white damage.
Yellow damage
When you miss a special, or it gets dodged or parried, approximately 82% of the energy is returned. That is, the miss cost 18% of the energy of the attack. On average it'll take you 1/(1-miss) swings to land the attack, of which 1 costs full energy E and the rest cost 0.18E each. Average energy cost is F
F = E*(0.18 * (1/(1-miss) - 1) + 1)
F = E * (0.18/(1-miss) + 0.82).
dF/d(-miss) = -E * 0.18 / (1-miss)^2
dF/d(-miss) = -E * 2/9 (miss = 0.1)
That is, 0.22% reduction in cost per 1% reduction in misses.
(Less math approximation: missing increases your energy cost by 20%, missing 1% less reduces your energy cost by 0.2%)
Since your yellow DPS is cooldown limited, a 0.22% energy saving per 1% hit means 0.22% yellow DPS increase.
Tying it together
This depends on how much of your damage is yellow and how much is white. According to the cycle i modeled I had 39% white, 61% yellow (34% shred, 20% rip, 7% mangle).
Total damage increase from 1% hit: 0.39 * 100.8% + 0.61 * 100.22% = 100.45%
That is, 0.45% damage increase.
I'm not going to run through the full math for other stats, but 1% crit increases 80% of my damage (no rip) by a bit over 1%, and increases my combo point generation and thus yellow damage by about 0.7%, for around a 1.25% damage increase, around twice as good per rating point. Agility and Strength are even better of course, my sheet puts them at about 3 times as good as hit rating point-for-point.
What am I missing?