The Wrestling Observer/Figure Four Weeklyis now saying that the latest numbers are looking much lower than the 1,000,000 they last reported:

UFC staff was told early last week that the UFC 117 numbers were looking to be just under 600,000 buys, significantly down from fight night expectations. I had actually predicted 550,000, though when the show was over the feeling I had was that it was an easy 1 million buys show. It should be noted that our trending numbers plus sources outside UFC are tracking it closer to 1 million. Part of the issue is that there are wide variations throughout the country with some systems showing huge numbers and other systems showing much smaller numbers. It'll be several weeks before we get what we can really call a solid number.

MMA Payout comments on the difference between trending numbers and estimated numbers:

Trending numbers are based upon pre-fight indicators (e.g., live gate, television ratings, or Google search frequency) that are known to have a significant correlation with PPV buy rate numbers. When a fight is said to be "trending" towards a particular number the analyst is essentially saying that the pre-fight indicators are currently at levels that would suggest the PPV buyrate will be X. Trending numbers do not incorporate any sort of actual number received from a cable company. Estimate numbers are based upon actual reports from cable companies. These typically take a little longer to report, because the cable companies need time to gather the purchase data from their systems. Then, once reliable base numbers have been gathered, the company will extrapolate those initial figures to give an estimate of what the overall card has likely produced from a buyrate perspective.

Cage Side Seats still sees big things in store for a Chael Sonnen/Anderson Silva rematch:

Based on the legend of this fight and another strong hype job, I suspect that a rematch could easily hit 1 million buys. I don't think it could hit UFC 100 levels, but it wouldn't shock me if it ended up as the biggest Lesnar-free UFC show in history.

The thing to keep in mind is that even if the early estimates were insanely optimistic, 600K is still a dramatic improvement over previous Anderson Silva headlined UFC's.