Jim,

I don't know anything about Grandis, though I have owned and worked on a few other Italian roadies. All of them have come to me with the steer tube cut to fit a 40-ish mm headset, perhaps with a small added spacer allowance to allow a front center pull to be used. I can see how with a threadless fork you could get some added handlebar rise if you leave the steer tube long. And this would also apply if you used a threadless stem on a threaded fork. But with a threaded fork and a quill stem there are some other constraints.

1. You need to have the portion of the quill that will expand, be it conical or wedge, to apply pressure below the threaded area of the fork. This is what limits how high a given stem can be raised. The safety line is an indication of this state. If you don't do this there can be a stress riser in the steer tube material, and the threaded area has sharp edges which impair the strength of the steer tube to such stresses. Fatigue failures of steer tubes are the worry here.

2. Because of this constraint, in the past one would purchase a stem with a longer quill (such as a Nitto Technomic Deluxe or a Nitto Technomic to elevate the extension portion and the bar without quill pressure on the threads of the steer tube. This solution did not require an extended steer tube to "go with" or to provide support to the extended quill. A more recent solution is to use a quill to 1 ⅛" adapter to be able to put a threadless stem on the bike at a suitable height. Obviously this lets you more easily dial in your reach as you change saddle-bar drop.

3. If you can get a stem that positions your bars as you need them without the expanding quill end affecting the threads, there's no reason other than cosmetics to trim the steer tube or leave it long. But if you later want to slam the stem, the elevated edge of the steer tube will limit how far down the stem can be pushed, compared to a steer tube cut for a 40 mm road headset.

If you ride a small frame with a Columbus steer tube, there is often an internal butting to strengthen the steer tube/fork crown interface. This also can limit how far down you can slam a particular stem. On my 51 cm c-c Masi frame it's a problem.

Was this Grandis f/f a NOS frameset? If not, the fork seems not matched to the frame. It could be that the fork was never intended for that frame. If so, trimming the fork might not be a good idea if the steer tube threading does not reach down far enough into your head tube. Theoretically you can have new threads cut, but they need to match seamlessly with the old threads to make sure you can tighten the headset properly. Could take some significant craftsmanship to accomplish that, and they really only get one try to do it right.