A friend of mine told me that studying the War of the Roses at university made SoIaF a little predictable when he got around to reading it, which might be an indicator of how closely based it is - or a suggestion that all dynastic civil wars between feuding noble houses tend to play out in the same way.
I'll try and catch him and get some more detailed answers out of him.
I've heard this as well, and did some googling about and came up with this. This is the internet, so someone has already done the hard work, we just have to find it, lol.