The change of head angle (which might be about 1.5* assuming some common dimensions) is but one factor in determining handling. The rake is another and the rake, tire diameter and head angle will result in a trail number. But this still is not the complete story. The weight balance between the ft and rr comes into play as will the center of mass shifting up/down/fore/aft. One can make some basic predictions but until the fork is actually installed and the bike ridden exact opinions () won't be fully known.

I would advise a headset and stem change over to threadless instead of threading the steerer. This suggestion is fully reversible with no loss of fork value or possible integrity. It is prudent to consider not threading a steerer. many have tried and had less then acceptable results. Especially with an AL steerer, remember AL tends to crack and not bend or stretch on failure. There's a reason that the AL 1" steerer forks didn't last long in the market place and why no ones (that I know of) were ever threaded OEM. Andy.