Hmm I do wish we could see Vettel in a car of similar speed to the McLaren or Ferrari of the last couple of years, to see how he really stacks up in a different situation to just running off into the lead. I honestly think he would struggle, however I don't think he's as weak at overtaking as everyone assumes, especially when it is often said that the Red Bull has more trouble than the average car in turbulent air and how Red Bulls usually have slow straight line speeds which surely must hinder overtaking attempts.
I agree that it would be interesting and I think you make a great point about the Red Bull struggling on straight line speed and its super aero package going a bit skewif when following other cars. The thing with Vettel that has made him so much stronger than all the other drivers since the later half of the 2011 season is that he's accepted his weaknesses and made dam sure that his competitors haven't had the chance to take advantage of them. Sometimes he cracks when pressured. Solution. Make sure no one gets near enough to apply the pressure by put in some blinding early laps and then pacing the opposition. Sometimes he gets caught up in silly incidents in the pack. Solution. Make sure he's never in the pack by sticking it on the front row every race weekend.
Alonso and Lewis could certainly learn from that.