I was trying to look at this from another angle, and a thought occurs. This is supposed to simulate f-duct advantage, correct? So, we look back to last season in Barcelona, where Button was trying to pass Schumacher into turn 1. He couldn't do it despite the f-duct (this is just one example). Perhaps therefore this won't be quite as foregone as we might think - the savvy drivers could still block, emphasising a different skill set to before...
wtf?! you axtually thought about it? i thought the f1 way was
to take like a cat to water any change in our sport, and
collectively pretend we all agreed
with it when it works and prooves us all wrong... 
maybe now everyone will
THINK and stop this silly witch
hunt.
Sorry mate, I'm sticking with the witch hunt for now

@Scotty - yes, there were plenty of examples of where the F-Duct just wasn't enough to get past. But, it's a fact that the F-Duct worked. It was able to eventually stall the rear wing by the driver disturbing an air flow, directed through a duct and out the rear wing to cause separation of the upper and lower air flows and thereby stall the aero effect of that rear wing. What the driver will have this year is an immediate and direct opening created at the rear wing which will a) immediately stall the rear wing and b) there will be less drag - an opening created where there wasn't one before. This is going to be way more effective than the best F-Duct of last year.
On top of that, there was always a difficulty last year once you got close to any car caused by the incredible turbulence created by the blown and DDD. As I mentioned earlier, remember Seb's front wing dancing about as he got close to Jenson - just before he speared into his sidepods? Well that is all gone now. So, what we have is a way more effective F-Duct and none of the turbulence from the DDD etc.
The advantage is totally artificial - it is given by a 3rd party who has nothing to do with the car or driver. If we had a race and two cars stopped 50 metres before the finish line, it would be like saying the Stewards can help push the car behind, but not the one in front.
IMO its biggest and worst effect wont relate to passing, it will be that it allows a clearly slower car/driver, to keep up with a better faster car/driver.
And, in case you forgot - "Manoeuvres liable to hinder other drivers, ..... are not permitted."
Me and the other witches say "Get rid of this stupid rear wing rule ASAP"