Why you shouldn't mindlessly spam Execute
after 20% on a raid boss to optimize your DPS:
(It does not matter whether the Attack Power values in this document are unbuffed or buffed.)

The vertical line signifies the static rage cost of Bloodthirst.
It is the data to the right of this line we're interested in when comparing Bloodthirst and Execute.
The upper line shows the DPR comparison between Execute
and Bloodthirst when the former is fully improved by talents.
The lower line signifies the standard rank 5 Execute.
You can for example gather from looking at the graph that if you have 2200 attack power
and improved Execute, you should always use Bloodthirst if you can (rage, cooldown may be in the way).
The coming examples show how much damage you gain/lose by using Bloodthirst
before you spam Execute, with a set amount of AP and a set amount of rage used:
2600 AP Fury 0/2 Imp Execute
1) 1875 damage for 100 rage using Execute only.
2) 2595 damage for 100 rage using Bloodthirst, then Execute.
Style 2 is 38.4% more effective
2600 AP Fury 2/2 imp Execute
1) 1950 damage for 100 rage using Execute only.
2) 2670 damage for 100 rage using Bloodthirst, then Execute.
Style 2 is 36.9% more effective.
_______________________
2600 AP Fury 0/2 Imp Execute
1) 1050 damage for 45 rage using Execute only.
2) 1770 damage for 45 rage using Bloodthirst, then Execute.
Style 2 is 68.6% more effective
2600 AP Fury 2/2 imp Execute
1) 1125 damage for 45 rage using Execute only.
2) 1845 damage for 45 rage using Bloodthirst, then Execute.
Style 2 is 64% more effective than style 1.
_______________________
2000 AP Fury 0/2 Imp Execute
1) 1425 damage for 70 rage using Execute only.
2) 1875 damage for 70 rage using Bloodthirst, then Execute.
Style 2 is 31.5% more effective
2000 AP Fury 2/2 imp Execute
1) 1500 damage for 70 rage using Execute only.
2) 1950 damage for 70 rage using Bloodthirst, then Execute.
Style 2 is 30% more effective.
1300 AP Fury 0/2 Imp Execute
1) 1425 damage for 70 rage using Execute only.
2) 1485 damage for 70 rage using Bloodthirst, then Execute.
Style 2 is 4.2% more effective
1300 AP Fury 2/2 imp Execute
1) 1500 damage for 70 rage using Execute only.
2) 1560 damage for 70 rage using Bloodthirst, then Execute.
Style 2 is 4% more effective.
1000 AP Fury 0/2 Imp Execute
1) 1425 damage for 70 rage using Execute only.
2) 1350 damage for 70 rage using Bloodthirst, then Execute.
Style 1 is 5.5% more effective
1000 AP Fury 2/2 imp Execute
1) 1500 damage for 70 rage using Execute only.
2) 1425 damage for 70 rage using Bloodthirst, then Execute.
Style 1 is 5.2% more effective.
1000 AP Fury 0/2 Imp Execute
1) 1875 damage for 100 rage using Execute only.
2) 1875 damage for 100 rage using Bloodthirst, then Execute.
You might ask - what if I wait and save up more rage before I click that shiny Execute button?

Execute's rage efficiency goes down the more rage you have. So unless your rage generation is gargantuan, the
safest bet is Execute whenever you can, more than a few large ones.
An additional point: If you have less than 1000 AP, just use Execute.
// Slafsinator - EU-Magtheridon