Dang, cainsight! The best I've ever done is 69.7 (or was it 69.9? Never been back to those heights so I don't quite remember the breakpoint) on the 40-some miles from Oakland to San Jose on 880, on a warm day in the right lane... So jealous.
The San Mateo bridge always seems like a fight for me, since the wind is generally cross. When I'm going east it's late and there are not many other cars to break it up; when I'm going west there's the hit from that big hill at the end. It's my favorite bridge in the Bay Area still.
For drafting ("surfing"? I always stay 2-3s behind), I've found that the big square trucks and tour busses work way better than gasoline tankers. And yeah, a massive SUV is better than nothing. A sedan is better than nothing. A Hummer is worse than nothing, though, since they go way fast.
I did hang gliding for awhile, and they taught that even a tiny bush can cast a shadow of rotor (messy air) when the wind is going 60-some mph for hundreds (thousands?) of feet. In the Insight, too, you can see the effects of even a tiny car as a windbreaker.
I've thought about riding along in the wind-sheltered spot in the next lane over from an SUV, like geese in a V, but that spot is unfortunately the blind spot.