According to the TFL website this should cost me �2.50 to do this, but no! Look closely and you'll see that at certain times it only cost me �2.00.
Puzzled by this I asked the guy at the ticket office who explained that if you travel using PrePay Oyster after 7pm in the evening (as my journeys were) then it becomes even cheaper. The most you'll ever pay - even on a Zone 1 to Zone 6 journey - is two quid! Good eh? And if you ask me, LU don't publicise this enough, so I thought I'd do it for them here.
Anyway, I picked up a 'fares' leaflet at the station which did indeed confirm this if you scrutinised it enough, and then went back to the TFL website (which I think is badly organised and very confusing to use) to find the same info and eventually after much digging around managed to do so - but it's not that obvious.
Looking back at my usage screen, all the �2 journeys are indeed after 7pm in the evening ... except for one! It still think there was a Wimbledon to White City journey made on Friday 25th March at 11.48 in the morning (you can see it in the picture above), and it still only cost me two pounds. I have no idea why.