Impaired and 0.08 are two different charges in the criminal code. All the police need is reasonable grounds to believe your ability to operate a motor vehicle is impaired by drug or alcohol to charge you. In most cases they won't even get a road side sample as it just hampers their case for your impairment. "If you were certain he was impaired, why did you need a roadside sample?"
The breath demand is what you will be read when it's time to go downtown and an actual breath tech has to take that sample. Within four hours of time of drive to get the certificate they can use as evidence in court, however an expert can come in to extrapolate the sample if you pass that window.
This impairment will always be different for different people, so don't get hung up on the BAC.
Also the penalty for refusal is the same as impaired or 0.08 so never refuse. Refusal can include pretending to blow, or purposely blowing out the side of your mouth etc.. as well.
Honestly if you drink, just don't drive it's that simple. You are the worst person to try and assess your own level of impairment and your buddies are not trained professionals and are most likely drinking with you. If you need any motivation for that read this article:
http://www.cjme.com/2016/06/09/van-d...g-and-driving/