The most powerful 991 at the moment is the brand new 560hp 991 Turbo S but we all know we have plenty more coming. The GT3 RS, the GTS and the monstrous GT2. The new GT2 is expected to get around 600hp which will put it up there with the fastest cars in the world. The rendering below done by Perfect Finish looks like a very good guesstimate to me and I cannot see it being very different to this. This is going to be one HOT Porsche!