Hi Stuart,
Your iTunes is showing 11.3.x ...current version is 11.4(18).
I suspect therefore that your Mac is pretty much giving you the genuine answer to the problem.
If you go into App Store on your mac (Applications -> App Store... or just click the logo on the dock), then go into updates. What shows there ?
The update window looks a little bit like this, although obviously it won't say "No Software Updates" if there are some !
Keyboard has improved, lot of plus points including the self timer on the camera. Bad side? Performance; since hardware is still the same but overall, not bad.
Indeed, lots of good stuff in 8.
Performance is fine on the 5 series, it doesn't need a 6. Good to hear it works fine on the 4.