This is a topic near and deer (lol) to my heart as I live and ride around lots and lots of deer.
Without turning this into a science project, I'm interested in discussing best practice in terms of dealing with deer.
Jon, you say if you were going a bit faster this would have turned out bad. What if you had been going faster and didn't slow? What we, as riders, are trying to avoid is the intersection of two lines; our path and that of a deer. Our path is our speed and stopping or accelerating potential as well as what little maneuvering could be done in the time between recognizing an oncoming deer, if any, and potential impact and the deers same potentials.
I have had it told, not suggested, told to me by one rider with well over 100,000 miles and some 20 years riding that when you see deer, you speed up. This guy is an engineer and his point is that, like hitting a bullet with a bullet, the goal is to reduce the chances of collision with speed. You are giving them less time to react, less time on the 'X' that point where you could hit them, or they you.
I've heard other riders say to just try and not react to the deer, focus ONLY on what is a safe path for you absent the deer meaning don't take action that WILL result in you running off the road or washing the bike out or crossing the center line when you can't see if the way is clear of oncoming traffic. The point was to operate the bike so that it will stay on the rubber and hope the deer is gone or, at least hope for the best in a collision with him, when you get to it vs. taking action that will cause you to lose control whether you hit the deer or not.
I haven't had any close calls yet with anything bigger than a squirrel and, to me, part of the battle is the mental preparation of what I should be trying to do when the time comes, akin to entering a corner too hot and working your skills with certain actions in mind, to save it rather than just panic, unload the suspension and guarantee a crash.