I own one of each(Smith-Corona 1903A3, Eddystone 1917), and if I had to shoot a HighPower Rifle-style match at distances greater than 200yds, I would choose the '03A3 for the following reasons:
- The very thin, sharp, narrow front sight blade(it's just a strip of stamped sheet metal, barely qualifies as a "post"), which IMO allows me to draw a finer sight picture on a small, distant target - yes, the '03's front sight was known to break under harsh handling in the training fields, let alone the battlefield, but if this is an issue at your match, you've got the wrong gun for the wrong game...
- The rear sight, which allows repeatable click-adjustment for doping windage and elevation. Yes, in the heat of battle you should just hold-off for "Kentucky windage" rather than fiddle with your sights, but an ordinary shooting match ain't "the heat of battle," and holding-off instead of "drawing a fine bead" might cost you just enough shots dropped out of the "X-ring" to lose.
As a "battle rifle," the 1917 has a lot of advantages over the '03A3 - a sturdy, bold front sight that is well-protected, an extra round of capacity, stronger primary extraction due to the cam angles on the bolt locking lugs, slightly faster bolt operation due to the "cock-on-closing" design, and the rear peep sight with protective wings integral to the receiver. However, the old canard that "the range is not the same as the battlefield" works both ways - and in a target match on a "one-way range", IMO the '03A3's "target rifle" features give it an edge.