Moondog, thanks for your recs. Called both Mr. Tian and Mr. Jie - spoke to them both in Chinese - don't think they really understood English. Mr. Tian could not have been nicer and knew exactly the type of car I needed (ie, a van) - unfortunately, he didn't have a big enough vehicle and said he didn't know anyone who did. Mr. Jie, who was a little less knowledgeable, referred me to some company/colleague who quoted me RMB1000. I ended up downsizing our group to 4 people and going back to Mr. Tian, who had quoted me RMB500 for the day. (I didn't negotiate - just accepted his price, as he had said his car was the largest type of sedan you could get in the country.) We agreed on a 7am pick-up at the Marriott Courtyard. Turned out he couldn't make it and sent a colleague (he didn't give me a heads up but his colleague showed up early at 6:50 and it all turned out fine).
Our driver Mr. Meng was terrific. He spoke some English but not much, so we spoke to him in Chinese mostly.
What we liked about Mr. Meng:
1) He was waiting at the hotel at 6:50 for our 7am departure. (But we didn't actually leave until 7:15 as it was like herding cats to get our group together! - actually, one person in our group was stuck on a conf call for work, so we were delayed.)
2) He had picked up bottles of water for our group.
3) The car was an Audi, so it was a smooth and comfortable ride. His car was a little tight for our group of 4 (3 were big guys well over 6 ft tall) - we were definitely cramped, but his car would've been very comfortable for 3 passengers.
4) He's a good driver - very smooth driving.
5) An hour into the drive, a couple of the guys in the group needed to take a bio break and he took us to a gas station that he knew would be clean. He bought a little bit of gas at that gas station just so our group could use its facilities. At Mutianyu, he also pointed out which toilet facilities would be cleaner (the ones inside the gates for the cable car ride - makes sense).
6) At Mutianyu, he advised us to get the cable car and toboggan tickets. We were so glad we did - the toboggan ride all the way down the mountain was definitely one of the highlights of our trip to the Great Wall.
7) He proactively told us where he would be waiting and gave us his cell phone number. (He never actually moved his car from where he had it parked.)
8) He proactively asked if we wanted to see any other sites in the area (ie, temple or lake) as well as in Beijing - he drove us past the Bird's Nest and Water Cube, pointed out the new *7 star* (how 7 stars is possible, I don't know) hotel under construction, pointed out other landmarks/interesting buildings on our way back (Lama Temple, hutongs dating back to the Ming and Qing dynasties, etc), offered to take us anywhere else we wanted to go in Beijing that day (but we declined - we were wiped out after the Great Wall).
We really liked how extremely thoughtful and considerate he was, and would definitely recommend him.
As for the time that we spent traveling to and from Mutianyu...
7:15am - on the advice of our Forbidden City tour guide (she was awesome - will give her contact info in separate post / trip report), we departed from the Marriott Courtyard early to avoid the crowds. It took about an hour of driving before we were off highway and less than 30 min of local streets (past lots of orchards) to get to Mutianyu. From door to door, it was just under 1.5 hrs including a 10 min pit stop at the gas station for a bio break. It was great we left so early because when we arrived, there were fewer than 20 people there in total and the air temperature was cool. We practically had the place to ourselves - we'd see a couple people here or there. There were only 4-5 people who were ahead of us who passed us on their way down when we were going up. By the time we left at 11:30, the place was getting much more crowded (though not swarming with people as it was a Thursday) and much warmer.
8:45-11:30 - explored the Great Wall. That was about as much as we could do - lots of steep steps given we went to a couple of the watch towers, including the highest one that's to your right when you get off the cable car. The views were amazing, and we took lots of pictures. Then we headed back to the cable car area, where we took the toboggans down.
11:30-1 drove back to the hotel. It took an hour before we reached Beijing. Then another 30 min of driving within the city to get back to our hotel. We paid Mr. Meng when he dropped us off at the hotel. And Mr. Meng seemed very happy with the RMB500 for our 5 hr trip.
Mr. Meng (4th tone for those who know Chinese tones) 139-1190-7931
Mr. Tian (2nd/3rd tone) 136-9-153-0178