I have asked that question here, at my LBS and I emailed Ritchey when I purchased a carbon fork with 1 inch aluminum steerer tube.

For the most part I do not get a straight answer, but this is what I have gleaned:
- 40mm is the maximum for a carbon steerer tube.
- for an aluminum steerer it gets quite grey. Certainly a 1 1/8" steerer would provide more security with more spacers than a 1" steerer with the same number of spacers.
- if you are using the bike to race, then it would be wise to keep the spacers to a minimum. However, for everyday riding more spacers are possible.

My Ritchy fork, with 1" aluminum steerer, has 80mm of spacers, using a 90mm Ritchey stem at 17 degrees (up). When I ask "is it too much?" they say, "I've seen more"

Soooo, less is better for sure. Speaking strickly about aluminum steerers; you would be more secure with a 1 1/8" steerer than a 1" steerer and if you race try to use as few as you can. If you do not race, then it can add more spacers to get you at the height you're comfortable with.

Some will state that your bike is not the correct size. Well, this bike I speak of, with the 80mm of spacers is a custom built steel frame. Another LBS, took my measurements and supplied the company to build a frame for me. Did they goof up? I don't think so, I was fitted on this bike several years later, as I had some neck trouble and what I have found is to run 80mm of spacers with a 17 degree stem.

My new bike, with carbon steerer, will have 40mm of spacers, 17 degree stem but the head tube is 20mm longer.

Hope that helps.