I don't see you having a probelm with the 6.5 with barnes X as long as you don't take shots over 150 meters and pace the bullets well. Barnes does have enough penetration but not enough whack for a big animal like a kudu at a distance.
With the 7 x57 I would suggest the 175 grainers for bushveld they work well just like the old 303.
-------------------- "Sleeping under the African sky I can see nothing wrong with this world!"