I put a lot more stock in torque than speed (obv). Luckily when I bought the HobbyKing kit with the 5065 motor (?) I inadvertently got torque rather than speed.
Torque is a lot more useful than speed in Wellington (hills, wind)… and my commute is only about 3km.
In a few days I will probably have a better answer to this thread. I am interested to find out what @Deckoz is talking about with downhill boards how riding down hill on them is different then a powered eskate.
I tend to be riding faster than I can run off on a regular longboard every time I go out anyways, so I want to go faster than that for sure when I am done building. There are only a couple hills around me that can get me going fast enough that I feel the edge of that thrill that I used to get bombing mountains.
Riding an eskate is something I am going to have to learn for sure, but I feel like 20 years of bombing hills and never really pushing past my limits even though I’ve been clocked past 55mph more than a few times while always feeling in control for the most part, is going to serve as a good foundation for learning to control my eskate at speeds that I can really only get to on one hill near me, but instead pushing that (responsibly) elsewhere too, just not as-fast as I used to go. I think 35-40 mph on a wide open and closed off road will be enough to satisfy my need for speed initially. Past that, I think I have a real reason to pull out my leathers and fullface.
To answer your original question, I rationalize it like this: I have experience to learn from. I know it’s a ton of fun going very fast. I have had some pretty gnarly falls, but as long as you wear the right PPE, you are smart about how and where you push the limits, expect the unexpected and ride fast defensively, the falls don’t have to be as bad as they could have been… And it’s a crap ton of fun at the same time. Because the best I can do where I am at now is go maybe three times as fast as I can push for maybe a hundred feet or so, I want to be able to do that and more, but not on the same stretch of land over and over.
I think this is what he was talking about or at least a small part of it.
That makes complete sense! Thanks for linking that… This is one of the reasons why I am building on my downhill board that I’ve been riding for 12 years… Lol. I’ve done a test ride on it with the components installed with no power, and it’s way different for sure- but at least it’s a shape and concave that I am intimately familiar with, and it felt good. The board felt like something I could easily get used to being much heavier and powered, opposed to one of my other less ridden downhill boards- some of those I just catch my feet on the wheels out of nowhere or step off the deck onto the cutouts not expecting it or just generally don’t have the feel for controlling them like the one I’ve been riding for years. It sucks, I love the other boards, and they are great boards, but I don’t even feel comfortable on them going 20mph in my neighborhood, let alone bombing anything mildly substantial.
So, I hope the addition of the battery doesn’t change the feel of my favorite board that much. At least I know it will be better starting from a known and comfortable foundation than bolting motors to one of my less ridden downhill boards that I am already nervous on without motors. If that were the case, I’d be gearing for 25mph max.
Most healthy people can sprint at 13-17mph.
Sadly I broke my knees about 10 years ago so my top-speed for sprinting has come down a fair bit. In fact my 10km (running) time is at my new “sprinting” speed 
I do city commuting mainly so past 22mph I start to get nervous. I don’t see myself needing to go faster than that. Possibly if I over safety gear myself I’d be willing to go faster but I haven’t hit max speed on my board yet.
My first build has a 6S lipo setup and it is a good cruising speed as long as you don’t have any really steep hills. My next build (in progress) will have 10S because I want my board to go a little bit faster than I actually want to ride it. I agree that 15-20 MPH is plenty fast for a skateboard.
downhill is free, down hill is gravity, esk8 is power under your feet, that power can make your board not under your feet, or put you in an uneasy position over the board. DH is all gravity, and the board never tries to leave me… if that makes sense? plus what @ROFEN13 quoted previously, its just the whole riding experience is different