I believe the reason you have not received a reply is that there is no short answer to your query. There are individual morphology factors and personal preferences that vary the angles racers prefer. In general a racer may like slightly stronger edge angle set-up for slalom and slightly softer edge angles for speed events.
Most skiers are asymmetrical and have different needs for each foot/boot. On the frontal plane I consider four angles when assessing and modifying equipment with a very set methodological order. First the foot/ankle position on the longitudinal plane (adjustments made with footbed and boot board), second, the cuff alignment to match lower leg shape, then boot sole cant to position knee in desired location, and lastly the base bevel. All four of these parameters affect frontal plane performance (edging).
Elite racers will often test tunes and bevel angles for different courses but likely not mess with boot mods for a particular course, though they may have a different boot set up for different disciplines.
hope this helps.
one note: you asked about changing shaft angle changes. the cuff angle or shaft adjustment is used to accommodate the curvature of the skier's lower legs rather than to affect knee position. Knee position should be corrected with sole cant angle.