I bought the 70-200 f2.8 IS USM II right after it came out, on the belief that it would be the best available for ten years - so far, no disappointment. I'm looking at the 5D III the same way - get it right after it comes out, and you'll have 'the best' for a solid five years. The easy improvements have all been wrung out of DSLRs - it's all small increments from now on. There's no point to annual body upgrades (like there was in the 10D-20D-30D-40D era) because the 70D or 7D II or 5D IV will not be a quantum leap - it'll be what you have now, but better.