Roy:
Congrats on booking a safari. I've got a number of them under my belt. Be advised/cautious that depending on what country you're going to or even what province within a country, the 6.5 may not meet the minimum caliber legal requirement. Most, not all, have a minimum caliber requirement of anything 7mm diameter or larger for PG. Some countries or provinces MAY allow for the smallest species, like springbok, duiker and up to impala it may be a wiser choice to meet the 7mm min so there is no potential problems.
While "local" hunters may be allowed to use smaller caliber rifles, the rules can be a good bit different for the foreign/international hunter. Best to contact your PH/Outfitter directly for their recommendation. It's not so much an issue of the 6.5 being effective or not, it's more of a legal issue.
Michael
