7D with 17-85 EFS

I've been debating on pulling the trigger for a 7D purchase. Would be upgrading from my 20D, which has served me well for six-plus years. Wouldn't get much on the resale of the old camera so I plan to give it away .. so I am still looking to justify this purchase.

What would be the most striking upgrades in technology between these two models and would it be acceptable, at least at first, to use my 17-85mm EFS lens, before bumping up to a newer lens? Will I notice a significant bump in image quality, even using this older (but good at the time I got it) piece of glass?