70 in 6400 has been on sale at Costco all month for $1999 but just checking in the other day and they didn't have any in stock at my outlet. That has been my target TV - I'm in a very similar boat than Mysterious, But I have been a little hesitant in pulling the trigger on the Sharp 640 or 6400 because of a lot of picture quality issues that have been reported on its forums. However, I take a lot of those with a grain of salt - I just think when a TV gets to that size, uniformity of perfect picture quality is really hard and they have not perfected it. So you get uneven lighting, etc. At this size, I'm not sure the premium you will pay for the Samsung and higher brands is worth the tradeoff.
The 65 in Samsungs will get you a completely stripped down version for 2k without even internet access and with minimal bells. And I'm not certain the similar sized TVs at 50-100% premium have enough of a picture improvement to justify the price difference. For example, take a look at reviews of the higher end larger Samsung forums, or the higher series Sharps, and you still see enough complaints to confirm my theory that you can always pick large TVs apart on some level.
So that brings me back to Vizio. I've had a Vizio 55in 552. Been moderately happy overall, but extremely disappointed in one flaw, a smallish dark discoloration that I've never been happy with (but others can't even see). Swore to myself that I wouldn't get another Vizio but these new lines seem to be amazing and are right at the price point of $2k for the 70 in. I posted some more details on the Vizio 70 E701i-A3 forum. However most people say Vizio takes forever to get them to market so I wouldn't hold your breadth on when it will appear.
For my 2 cents, I'd go with the 70 Sharp 6400 from Costco today, and likely the Vizio assuming it comes out before Christmas and is as good as the review fro the 60 in that was posted recently. I wouldn't go smaller to upgrade in picture quality, as I think the size differential is much more dramatic than the picture improvement.