I'd like to reemphasize that if you donate to multiple effective charities you are doing awesome stuff. Switching from average charities to a diversified portfolio of effective charities can make you hugely more effective -- it's like turning yourself into 10 people. Switching from a diversified portfolio of effective charities to the single most effective charity might make you maybe a few percentage points more effective*. That's not nearly as important as doing whatever makes your brain enthusiastic about effective altruism. The point I'm made in the parent comment is not of practical concern.

*I am making up these numbers -- don't quote me on this.