Hook, go back to the nballistic tables above and use a pocket calculator. If you look close, you will see the 156 – 160 gr bullet ballistics are taken with very different barrel lengths. Claimed factory ballistics were just as off here as they were in the USA.
The English indeed claimed 2300 fps for the 160 gr bullet, but from an outsized 28.5" = 72.4 cm long barrel, as found only on pre-WW1 military rifles, but rarely on sporters. The German DWM load ballistics were taken from the traditional M-Sch Stutzen barrel length of 45 cm = 18". From such a short carbine barrel the 10.3 g = 159 gr DWM loads claimed 640 m/s = 2100 fps with 2.75 g = 42.4 gr of the obsolete R1 powder, 680 m/s = 2231 fps with the high pressure 2.9g = 44.8 gr R1 load. The 1940 RWS handbook listed the same loads, crediting them with 668 m/s = 2192 fps and 710 m/s = 2329 fps respectively from a 45 cm = 18" test barrel, but 729 m/s = 2391 fps and 774 m/s = 2539 fps from an 68 cm = 26.8" test barrel. The lower pressure 2.75 g load is the only one conforming to modern CIP standards and apparently very similar to the old English load. IMHO getting 2300 fps with a 160 gr bullet out of the 6.5x54 M-Sch and a 18" Stutzen barrel is possible, but not much more.