If the 717 is 50% higher cost than the 709, i would definitely go with the 709. Besides the name change, i don't see much change, both support 8 hdmi inputs, 2 hdmi outputs, same watts per channel and the same features (at least audio wise) other than the fact the 717 doesn't have MultiEQ XT and instead drops down to 2EQ which is odd.
On the bottom of the site you'll find the differences of the 2EQ, MultiEQ XT and MultiEQ XT32.
I have a 709 and an 809 and while i haven't used the Audyssey on the 809, the 709 did a fine job with Audyssey.
From there you have the 818 which is like the 809, more power than the 709 or 717 but with MultiEQ XT32 instead.
If the 717 is 50% higher than the 709, i'd personally jump on the 709 in a heartbeat and even if they were the same price i'd still go with the 709 for the MultiEQ XT. If the 818 is the same price as the 709, i'd go with the 818. Newer isn't always better
On a side note, the 709 had an issue where it would not do HDMI pass through with audio for me. It was fixed after i did a firmware update. I have yet to experience any HDMI failures on either receiver.