Smoothing popcorn textured ceilings
We live in a 40 year old house that back in the day would have been considered higher-than-average quality. It has the original popcorn textured ceilings that were popular back then. Some of the ceilings have a bit of a "wave" to them here and there, as if some of the drywall has sagged a little over the years due to the house settling or whatever. This is NOT what I would call major sagging such as might be due to water leakage...just enough so you can see it when the light hits it right.
A few years ago we had about half the popcorn ceilings redone - the popcorn scraped off, some re-mudding (for lack of a better word or technical term), smoothing, etc., and painted. While I was relatively pleased with the work and outcome, I can still see some "waving" in the re-done smooth ceilings.
Now we're going to have the other half of the popcorn ceilings changed to a smooth finish. We will not be using the same contractor (not because of the ceilings, just because this job involves a whole lot of other work besides the ceilings).
Anyway, the point of my post, or question, is: In a 40 year old house with 40 year old drywall ceilings, how much "perfection" should I expect in a smoothed ceiling finish? I realize a totally level ceiling (short of new drywall, and even then...) is practically impossible, so...how much should "perfection" should I expect?
I'm hoping to hear from some of you folks that have had this done, how your's turned out, and how satisfied you are with the results?