I hunt extensively with a heavily modified Ruger M77 MkII. (As much as possible I have tried to make it feel, look and function like an english sporting rifle). The 6.5x55 is my FAVORITE rifle cartridge even though I use my medium bores to hunt with more. The 6.5 swede will penetrate very, very well and although its diameter is pretty small, I would put it up against a .30-06 on anything Kudu or smaller. For Eland, I would likely take my .375 H&H but only for insurance purposes. Keep the velocity around 2,600-2,650 and your pressures will be low and accuracy should be around 1-1.5MOA or better. This is more than enough for a 300-350 yard shot on deer sized game. I am lucky that once I glass bedded mine it prints a whole bunch of 140 grain Nosler Partitions right on top of each other. These are the bullets I would load if I were taking mine to Africa for Plainsgame
For the heavier variety of antelope or smaller (Kudu/Zebra Sized):
Woodleigh's 160 grain PP - If the twist in your rifle is fast enough
Norma Oryx 156 grain
Swift A-Frame - 140 Grain
These two if my safari were for game that is typically on the lighter side (Wildebeest sized):
Nosler Partition 140 grain
Swift Scirocco 130 grain
These are just my opinions but I like to always make sure my round will make it to the vitals from any conceivable angle I could ethically shoot at.