Picked up a 70-200 VII last Black Friday, rated a 8, it's maybe a 7+, but the deal I got I figure I paid for a 6, so net net, I I did ok. I think KEH rates more conservatively, and has a well deserved great reputation for outstanding service. Both are strong organizations, in general rental fleet is probably riskier due to usage, but they both allow returns.
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http://nikonrumors.com/prices/
This will give a good idea as to prices.