Livre d'Or

I've never come across this concept of utilitarianism or efficiency in donation
OK, well, you'd probably better read something by the people who actually promote this idea, not just me arguing against it! Giving What We Can is pretty much the motherlode. It has a giant picture of Peter 'let's kill all the expensive disabled people' Singer at the top of the page, which is probably another reason why I'm biased against its arguments, mind you.

I want to help cancer research for purely selfish reasons
I think if you were really being purely selfish, you could pretty much get away with gambling on other people being willing to donate to cancer research. Cancer is a well-funded cause if ever there was one, and it's just the sort of situation where "freeloaders" (in the game theory sense) can do extremely well. Honestly, even if you gave half your income to cancer research, that would be an immeasurably small proportion of what is spent on cancer research; it wouldn't measurably increase the chances that there will be a cure by the time you (chas vechalilah) succumb. Purely from a selfish point of view, your odds would be better if you spent the money (or took the equivalent salary cut) on spending as much of the year as possible somewhere with lower pollution and stress levels than London.

I strongly believe in self-interested altruism. People donate to causes that effect them personally and those close to them; I think that's ok, I don't think it's morally awful. That's one of the reasons why I disagree with the efficient giving folk.

I definitely agree with you that it's really hard to judge what amount to give to charity considering that we also pay tax, and tax covers a large proportion of expenditure that was traditionally thought of as the domain of tzedakah. I didn't want to muddle my argument too much by getting too deeply into the official charities versus tax issue, but it's definitely an aspect of this.