ERROR FIX
I made an error in my simulation about FB, I've computed Savage Roar 2 times. The program is now fixed. The new dps value are:
Free-SR/RIP+FB: 4991
Free-SR/RIP: 4838
About FB vs RIP question:
I don't know how tange simulator works and ability/buffs implemented, but let's do some math:
suppose 50% crit, hit and expertise capped (like in my simulation):
Base FB: 0.35*AP+1640 +extra_energy*(9.4+AP/410)
Now suppose that you have PI and crit meta gem and feral aggression and naturalist.
FB damage = Base FB * 2*1.1*1.03*1.15*1.1 =1.00*AP+4701+extra_energy*(27+0.007*AP)
Base RIP: (534+0.05*AP) x tick
Suppose you have mangle up and naturalist:
RIP damage = (764+0.0715*AP) x tick
Suppose that on average we will use FB at 40 energy (from my simulation you usually use it from 36 to 42 energy).
FB DPE = (0.025875*AP+121)
RIP DPE =(0.002383*AP + 25.5) x Tick
Let's assume a 25% damage reduction on the boss:
FB DPE = (0.019406*AP+91)
So we can find the number of tick to make them equal:
Tick = (0.019406*AP+91) / (0.002383*AP + 25.5)
AP APbuff Ticks
0 0 4
1000 1540 4
2000 3080 5
3000 4620 5
4000 6160 5
5000 7700 6
6000 9240 6
7000 10780 6
8000 12320 6
9000 13860 6
10000 15400 6
11000 16940 6
12000 18480 6
13000 20020 7
14000 21560 7
15000 23100 7
AP Buff = AP * 1.4 * 1.1 (Savage Roar + Unleash rage, thinking about a fix...)
Conclusion:
Considering that base RIP is 6 ticks and with glyph is 8 ticks and with 2T7 is 9 ticks (10 if they fix it), it seems that as ppl stated above RIP is always better than FB. BUT IT'S NOT TRUE. The reason is simple: RIP should ticks to be better. Suppose you have 8k AP. So from the table above you know that you need 6 ticks to make RIP better than FB, you also have RIP glyph. So your RIP ticks 8 times for 16 seconds. IF you have time to let your RIP expire obviosly RIP is always better, but usually that's not the case. Usually you take about 10 seconds to reach 5 CP. So suppose that you have used RIP but only 10 seconds are lapsed (5 ticks), what do you do? Ferocious Bite.
Other notes:
The table I wrote above is determinated by a simplified scheme. In my simulation I use a formula to find the energy value at wich FB is better than RIP for each tick, buff, debuff, etc..
the formula is the following:
energy_threasold=
fb.energy+((((rip.hit*(ap*0.39*(1+src)+4165.2)*(rem*2.0)/(12.0)))) + ((1.0*(fb.energy-rip.energy))*((1-red)*(((ap/14.0)*2.25)*(1+src)+(weapon*2.25+742.5))*(1+ret_m1*bdebuff)*1.3*(shred.hit+shred.crit*2*(1+pistinct_m)*(1+META*0.03)))/(1.0*shred.energy)) - ((1-red)*(1+ferocity_m)*(0.35*(1+src)*ap+ 1640)*(fb.hit+fb.crit*2*(1+pistinct_m)*(1+META*0.03)))) /(((1-red)*(1+ferocity_m)*(ap*(1+src)*0.002439+9.4)*(fb.hit+fb.crit*2*(1+pistinct_m)*(1+META*0.03)) - (((1-red)*(((ap/14.0)*2.25)*(1+src)+(weapon*2.25+742.5))*(1+ret_m1*bdebuff)*1.3*(shred.hit+shred.crit*2*(1+pistinct_m)*(1+META*0.03)))/(1.0*shred.energy))));
I hope the formulas talk by himself: ret = Rend and Tear, Meta is the +3% crit meta gem, src = 0.4 (savage roar), red is the damage reduction, weapon is the weapon damage (55.4 + 14 from stones) and so on.
About scaling:
I'm worried about our scaling in t8 and t9 raids, at t8 level we will have expertise and hit capped, and FB-crit capped (crit% > 50%).
Here is an example report that make clear the FB vs RIP question:

Ferocious Bite vs RIP, mob IS BLEEDING
Use Ferocious Bite for any energy value, Rip ticks: 1, Rip debuff counter: 17
Use Ferocious Bite for any energy value, Rip ticks: 2, Rip debuff counter: 15
Use Ferocious Bite for any energy value, Rip ticks: 3, Rip debuff counter: 13
Use Ferocious Bite for any energy value, Rip ticks: 4, Rip debuff counter: 11
Use Ferocious Bite if you have less than: 97 energy, Rip ticks: 5, Rip debuff counter: 9
Use Ferocious Bite if you have less than: 68 energy, Rip ticks: 6, Rip debuff counter: 7
Use Ferocious Bite if you have less than: 40 energy, Rip ticks: 7, Rip debuff counter: 5
Use RIP, ticks: 8, Rip debuff counter: 3
Use RIP, ticks: 9, Rip debuff counter: 1
Ferocious Bite vs RIP, mob is NOT BLEEDING
Use Ferocious Bite for any energy value, Rip ticks: 1, Rip debuff counter: 17
Use Ferocious Bite for any energy value, Rip ticks: 2, Rip debuff counter: 15
Use Ferocious Bite for any energy value, Rip ticks: 3, Rip debuff counter: 13
Use Ferocious Bite for any energy value, Rip ticks: 4, Rip debuff counter: 11
Use Ferocious Bite for any energy value, Rip ticks: 5, Rip debuff counter: 9
Use Ferocious Bite if you have less than: 95 energy, Rip ticks: 6, Rip debuff counter: 7
Use Ferocious Bite if you have less than: 47 energy, Rip ticks: 7, Rip debuff counter: 5
Use RIP, ticks: 8, Rip debuff counter: 3
Use RIP, ticks: 9, Rip debuff counter: 1
RIP: 12.4479% of total damage (SR: 15.8804%, Avg dmg: 15764.5, #/cycle: 0.965188)
Ferocious Bite: 7.6872% of total damage (SR: 29.6877%, Avg dmg: 14241.5, #/cycle: 0.659797, Average Energy Usage: 38)
N.B. the cycle starts-ends when you use SR.
@Tange: have you implemented King of the jungle and Berserk? Wich buff do you use? Haste? Boss armor? Armor penetration? If you give me talent/buff/stats info you use in your simulation I can try to figure out the difference with mine.