I don't know if I'm cautious because I'm a relatively new driver, but
speed demon just isn't my style, even though I've been told that I have a natural inclination to be this way due to my first house Aries stellium and third house Mars in Gemini.
In fact, my parents were much more worried about me becoming distracted while driving, and this is still my main weakness although I have attempted mightily to overcome it and
keep my eyes on the road. Don't get me wrong, my eyes aren't darting all over the place while I'm driving, but I get distracted by unusual sights and situations, and that split-second diversion can cause accidents.
I think I'm getting better, but darn it, I like to know what's going on around me! This is why I much prefer to be the passenger than the driver--because I can look around and do multiple things at once.
I have Mercury in Pisces square Neptune, and for the safety of the public I have chosen not to drive. I don't think this is a good placement for driving, I get easily distracted.
I have my natal Mercury in Aries, but it's also square Neptune with an orb of about four degrees--a degree less than my Sun and Mercury. Saturn is conjunct Neptune in my chart and squares my stellium with a slightly tighter orb, so I don't if its influence overrides Neptune--but like you, I get easily distracted.
Mercury is the ruler of my third house cusp, interestingly...
Arian Maverick