overpower should always be prioritized over BT if it's about to fall off.
If your world buffed/geared you're not supposed to mindlessly spam executes at 20%. With a fast mainhand or alliance side you're mainly going to get low rage executes, but the point is that BT and WW both do more damage per rage than execute if you're sitting at the 25 or 30 rage threshold. Ofcourse pooling the rage is generally a dps loss unless you get a swing close to the GCD so it's mandatory to have a swing timer.
This is a huge dps loss especially if you're using a 2h to spam executes. I'd like to mention that rather than swapping DW It's viable to stick with a BRE due to the proc and by utilising BT/WW you can get similar number or even better numbers on a short fight.
Also bear in mind that rage potting to full rage bar execute is a horrible waste. You can get a couple executes off when you reach 20% intially since you usually have some pooled depending how your swingtimer aligns with gcd. When a GCD is ending between swings, that's when you rage pot>BT>WW>Execute. Heroic Strike sub 20% is good too so you don't get capped while squeezing out a BT or WW.