I'm currently using a sector size of 15.000, which is waaaay more than default, but only increased max speed to 225. It takes a LONG time to get through a few sectors, and there are much less planets and asteroids around. That's not 100k, and yet space feels empty, so... careful with that.
Take note that you can't just scale sector size, max speed and range of weapons, as increasing speed also impact your performance and causes collision glitches (like being able to go throught a wall).
Also, because ships are also moving very fast, it's incredibly hard to hit small fighters for humans as the average range you must fire is way bigger, making AMCs and Beams... not that efficient really. Not efficient at all in fact (and totally useless for AIs unless you increase the AI accuracy). Simply put, that make missiles MUCH more interesting.
Switching all my turrets of my faction base from heavy-fast firing AMCs to much smaller turrets -but with lockOn missiles, turned out to be a very good idea. Even tho I increased the speed of AMCs to 5 times the max server speed (read: 1125), it's still big trouble hitting things. Having a huge cross to aim (and hide) your targets isn't really a good idea...
Don't forget to take those into account for balance reasons.
EDIT: Also forgot to mention that you can see ships from very far away. I can spot most ships in a 45km radius around me, making surprise attacks harder.