There's no minimum or maximum exposure for the highlights/backgrounds in a black-carded shot. As what you said, I usually do the spot-metering method, then pop in an ND filter(usually a Hoya ND400, though I think I'm going to grab a set of filters soon), calculate the proper exposure for both highlights and foreground before exposing for the foreground and 'black-carding' the sky. Depending on the strength of your ND filter or the time of the day, your highlight exposure may range from as shot as 1s to tens of seconds. Usually I might over-expose the foreground by a bit to achieve a more even exposure, but don't overdo it because usually the foreground isn't brighter than the sky, though in some cases it might actually look pleasing. And as always, do remember to shake the card!
245. Curvaceous
Had to do HDR for this one; the dynamic range is just too high. This place is amazingly difficult to compose though; I had to force myself to process this shot - I felt that the angle could have been better.
LOL, I was there today on the 38th floor. Made a trip there once back in February but somehow the shot didn't pan out well.
This was taken at the 23rd floor if I remember correctly.
