$7M would be closing in on nearly double the published record of just over $4M which happened at the RM Auction in London in 2008. That was for a pretty special car at the time - the former Park Lane showroom car from McLaren with pretty much only delivery miles on the odometer.
It's my understanding that values are hovering in the range that Senna has suggested right now but there could be a few special cars that might bring a higher transaction price like an LM or a GTR with fantastic race history. In fact I have heard of a few normal F1 where owner's appear to be fishing a bit in the $5M range.
The last public sale was #062 which was sold by Gooding in Monterey in 2010. That car went for $3.575M including Buyer's Premium to a California owner who then would have had to pay Sales Tax and Registration I assume. Total bill probably hit $4M for him when all was said and done but it was one of the few F1s that have been certified by California's BAR as being smog legal in this state so that likely helped in the desirability column for this particular owner.
Below is a chart that McLaren shared during a presentation in Monterey this past August charting F1 values over a period of time. The info presented is fairly vague, but you can pick out the high water mark from 2008 that I just mentioned and see where some of the other transactions they have been involved in have occurred as well.
To help add a little more context, the first two blips on the chart probably reference the sales of #011 and #073 through Christie's London auction in June 2003 and December 2003 respectively.