Hi Steve, I really like your shot from the Peak, it's a lot sharper than any of the ones I took! Did you use a tripod or were you just resting it on the railings up there? I didn't have a tripod at the time and thought I had it well placed, but I still got blur! Maybe it's my shaky hands, but from now on, I'm always going to use a tripod for any nighttime shots.
Using a tripod, I would go for ISO 100 every time. You don't have to worry about how long the shutter's going to stay open and you'll get the best quality pics.
I guess if the sky's clear like in your shot then a long exposure is fine because there are no clouds moving around. Did you catch the laser show while you were there? Maybe they only do it in summer. I have to go back again in June on a visa run and the last time I was there, last June, was when I first got my D80 so next time round I'll have had a lot more experience with it and hopefully get some better shots. HK's great in summer for clouds, but the heat's not so great!
With the aperture, I always thought using f22 would be the best, but then I found out that that can cause chromatic aberration, and I'm still not exactly sure what that is, but you don't want it
I think it's best to play safe and stick around f11 or f14. Depending on what lens you have, you can even go to f8 and still keep everything in focus.
When I go back in summer, I'll go back up there and I'll definitely use a tripod, I'll use my Sigma 10-20mm to get nice wide shots and then just experiment with aperture and shutter speed. Hopefully it'll be nice and dramatically cloudy again and with a stunning laser show thrown in for good measure...fingers crossed