I'm on the press brake band wagon. A couple of remarks above unlocked the secrets key to your success.
In order to get a consistent measurement between the flanges, you must gauge off of one end, whether it be with a CNC back gauge or fixed gauges. The CNC would be easier to set up and fine tune, but either will suffice. Besides the benefit of being able to fine tune the gauge dimension between the bends, you will be able to compensate for the difference in the blank size (which hasn't been discussed yet). By compensate, I am saying you can control where any differences plus or minus from your developed length end up. What I mean is one of the unequal flanges better suited to put the difference?
The other comments regarding the variable thickness you will be dealing with is high on the list of concerns. As was previously mentioned, you will have different thickness of parts from the same sheet or bar. You will have different results from the "with the grain" or "against the grain" even if the thickness is exactly the same. Again, this is where a CNC brake would shine. You would be able to fine tune the depth of the ram to compensate for the thickness difference of the blanks.
Trying to hit a perfect 90* in a single hit is like aiming at a moving target. You're not going to hit it every time. I always try to over bend the part slightly. It is way easier to unbend to 90 than it is to add more to the bend.
What is the source for the blank? Flatbar or sheet?
Wouldn't the OBI press hit at a high rate of speed?