I bought a 5D MK III to replace my 5D MK II and thought $3500 was too much for the differenc3, considering the features I use, so I returned it and bought another 5D MK II from the Canon refurb store for $1400.
Then, Adorama popped up with a 5D MK III for $2750 and that was the right price so I bought a second one. I also sold the 5D MK II for a $300 profit, and got a $56 ebay bucks credit.
I gather you are in the UK and can't easily buy from the USA, but I'd look for a deal on the 5D MK III.
You might also consider a 100mm L, mine really loves my 7D.
(I also tried a D800. Nice camera, but I found it impossible to buy equivalents to some of my favorite Canon lenses and resold it).