An interesting topic Shawn, with some interesting replies. Here's what I can add from personal experience with delivering bad news.
You should expect to have your results questioned, and rightly so. Don't take it personally, and be prepared to back up your statements. If you can't back them up, and you're not ready to answer questions about test techniques and data reduction and accuracy, maybe it's not yet time to speak up.
I've found it helps greatly to give "good news and bad news". For example, tell the team we have a problem here, but we can fix it by .... Don't get hung up on using your solution, the idea is to get everybody thinking about solutions.
Taking the boss for a ride can work wonders, but it can be a little scary too. Many years ago while testing engine oil system mods at the North American facility of a European manufacturer, we encountered compressor stall at max certified ceiling. The highest ranking European engineer on site was highly critical and skeptical. He stated that we weren't supposed to be looking for compressor stall (true), the Europeans had never had compressor stall (not true, we later found out), and we Canucks probably didn't even know what compressor stall was (that hurt).
At that point we convinced the old guy to suit up and ride with us to the very repeatable test point. We got both engines banging quite loudly. I really thought the European was going to have a heart attack. He looked distinctly ill all the way back down. However, he listened to us from that point on.