Same. I have to drive into London occasionally and the A40 has really narrow lanes as you get closer to London and no-one is patient with you!
I am OK with it but I'm much happier on a motorway or, randomly, a country lane. I grew up in a place where your main routes to anywhere were either motorways or back lanes, so I'm comfortable with both, but busy town/city centres are not fun.
DH, however, grew up in a big town so hates country lanes, so that's my job when we're on holiday!
Glad you did it OP - in hindsight that was the perfect combo - a bit of experience for you, but without it being the whole drive.
100kph is 62.5mph. I used to be a fast motorway driver and would happily do between 75-80mph. As I've got older, I just can't be bothered any more. It doesn't get me to/from work any quicker really and uses a lot more fuel (and of course is illegal!)
Now you'll more often find me between 60 and 70 in lane 1. It's much more relaxing, and quite frankly, there are so many middle lane hoggers out there, it's like having your own personal driving lane anyway!
I think 100kph is perfectly fine on a motorway. Lorries will be mostly speed limited to 90kph, so you'll be going quicker than them.