Regarding the DR-chase/fear of losing DR conversation, I have to say the system does a pretty good job of matchmaking once you get where you're "meant" to be.
For example, I think that I firmly belong in SR S (usually a few pips less than full, I am partial to a few delicate nudges here and there and I don't always do a good job of reacting quickly enough to incidents or staying on the track). I also think I'm an absolut mid-DR A. The thing about Driver Rating is that it's a totally fluid state and between races, sometimes you'll be paired with players who are slightly better than you and some when they are slightly worse.
There's not much point worrying too much about it, of you're spending less time practicing or playing other games you might have a temporary slip, or conversely, if you have favourable combos (or you just get yourself really dialled-in for a week or so) you'll see a spike on DR points.
The trick, in the end is to find that sweet spot where races are hard enough so that you are not able to cake-walk the opposition, but rewarding enough to make you feel like your time and effort is worth it. It'll always be a seesaw experience, unless you are particularly determined to refine your technique and philosophy.
As long as you play the game a reasonable amount each week, your DR & SR should reflect ON AVERAGE where you actually belong on the spectrum, and we all have an ability ceiling.
