The good news is that you'll have enough people for the HOV lane and travel inside the Beltway on I-66. Actually, as long as you're able to use the HOV lane, the rush hour would actually be faster. After 0930, when HOV gets lifted on I-66 (0900 for the toll road), things get bogged down for about an hour because everyone is jumping on the HOV lanes.

The worst part of the trip will be the wait to get on the toll road through the entrance toll booths. From the Sheraton, I would consider driving east to one of the other on-ramps at either Wiehle or Hunter Mill. They're bad enough, but not as bad as trying to get on at the Reston Parkway.

It also depends where you're going once you get into the District. I-66 dies at Constitution Ave and the Roosevelt Bridge and things can get pretty backed up.

I'm the eternal pessimist: I would give yourself a good 1:20 door-to-door, even with HOV. Unlike most other big urban areas, there are very few, if any, alternative routes. There have been times when there have been wrecks on just a couple of arteries and I literally have been cut off.

I was almost going to endorse wahoo's suggestion until you mentioned the entourage you're traveling with.