Some people may make arguments for morality based on things similar to Coherent Extrapolated Volition. I don't find those arguments convincing. I help people I don't know because when I think about the alternatives, I prefer the world in which one fewer person is suffering to the one where I'm better off in whatever way (e.g., I have more money in my bank account) because I didn't help. That preference is based on empathy, which was evolved, but I don't particularly care where it came from. At some point that preference gets outweighed by selfish preferences, which is why I haven't given all of my money away.

I don't think maximally helping others is a particularly good way to maximize your own quality of life unless you already want to do that. Both (a) and (b) are true, but if your goal is maximizing your own quality of life you're almost certainly going to do better if you focus on that directly. At least, in my particular case, there's some amount of warm fuzzies I get from helping people and from identifying as someone who tries to effectively help people. So in that way my quality of life is improved. But I think that if I wanted to I could get that amount of fuzzies at a lower cost.