Hm.. Why would you eat so much and why particularily in Africa?
As to the ROC, it varies with the ratio of excess power to weight.
Even if we assume that the climbout speed is pretty much the same for all weights, reducing the question to "what is the excess thrust?", we can't say much more since we don't know whether you've got an Eazy Rocket or a motorglider type of a powerplant. At least I can't simplify it further..