Aye. Point taken. All the online retailers seem to be having an ongoing chain/cassette price war at the moment so may have to stock up.
If I was upgrading cranks as well I'd have to think about it more, but as I'm sticking with the ones I have then I don't have to worry about the '4 arm' issue.
fair enough, just saying because it all adds up when you add in chainrings and chains etc...