There isn't much difference in "performance," whatever that means. But then there isn't as much difference in field performance among an even wider array of big game rounds as many hunters believe--as long as the bullet expands and penetrates sufficiently.
Which brings up another point. The original factory rifling twist-rates for the 9.3x62 (@1-14) and .375 H&H (1-12) are sufficient to stabilize very long bullets. But the original twist for the .35 Whelen (which factory rifles tend to follow) was 1-16, apparently to work better with lighter cast bullets, which Col. Whelen was very fond of. But the 1-16 twist is only sufficient to for stabilizing lead-cored spitzers of about 250 grains, though it will also usually stabilize somewhat heavier "blunt spitzers" such as the 280-grain Swift A-Frame. However, it won't stabilize heavier monolithics, the reason the heaviest 35-caliber Barnes TSX weighs 225 grains, and the heaviest TTSX 200 grains.
While of course a custom barrel with a faster twist would stabilize heavier monolithics, the predominance of 1-16 twists in .35 caliber commercial rifles (and not just Whelens) prevents major manufacturers from making such bullets. Meanwhile, the standard twist in 9.,3x and 375 caliber allows them to stabilize TSX spitzers up to 286 grains (9.3) and 300 grains (.375). Whether this makes a lot of difference might be debatable, but one of the major points of using "medium bores" is increased penetration on heavier game, which is exactly what heavier monolithics provide.
