well, if you calculate at least 550 bhp from the combustion engine (which is btw very pesimistic from what i have heared. All engine manufactures are very well pleased with the amount of the Power they can produce with the given fuel flows...) and 2x300 bhp while boosting, than you have a little bit over 1100 bhp while boosting
Michelin claimend that they will produce tires which have to carry on over 1100 hbp (over 4 wheels ) and these tremendous horsepowers suits very well to the times, Audi whrere doing in december with their new R18
So these new cars will be as fast as 2013, maybe a little bit faster