I think overall pace as a criteria of "doping" is way overrated. It more depends on the overall elevation profile of the race, the weather, how many teams are willing to take charge and maintain solid tempo over early stages, how many breakaways are there, etc. Top riders like Armstrong are in the front for a very small fraction of the Tour, so mathematically they don't contribute to overall speed much at all. During hot days, or rainy days the entire peloton may decide to soft-pedal for the first two hours. Or if there's a "nobody"'s breakaway and nobody wants to chase them. Sometimes there are significant winds that help or slow down the peloton as well.
I expect this year to be quite fast - less hills than usual, a lot of time trials. Of course time trials are usually even faster, but the lack of serious hills will keep overall pace high. You take the tough day in the mountain where they average 15mph, and you replace it with a flat sprinter stage where they go 30+mph, and it changes overall time much more than small changes in individual fitness of the riders.
Of course we also have less riders to begin the Tour, so that may slow things down just a bit.