Day2Day

How long is it okay to leave a cat alone for? I know a working day is fine, I know 48 hours is okay if enough food and water is down - but beyond that? Would four whole days be too much? Is it all down to the cat's own personality and a "how long is a length of string" type of question?

I am toying with the idea of getting a cat, but I am often away for 3 days at a time, occasionally more and I don't intend to mistreat one - it wouldn't really be practical to rely on having people available to look after it when I'm not about.