Power figures are often up to 15% lower than actuals. The V8s up to 820hp without KERS, there was only 25hp in it from the fastest to the slowest in Horsepower terms. However with the EBD and Coanda of the past 3-4 years the card lost up to 45Hp from the Crank to Axle as the electronics and exhaust contained that power. The fact that up to the end of 2007 BMW has a engine pumping out 815hp that lost 12% with the MES ECU introduction is testament to that. Also, if there was unrestricted development and allowance of some new 'green' tech in the V8s, Mercedes said their engine that ended 2013 could have done 22,000rpm with almost 950Hp. Thats an extra 2.4 to 2.9 seconds around Monza, without KERS.
Personally, i think the V6 combustion engine is getting closer to the 650 to 670 mark, with the 140 from the ERS, thats easily on par with the V8s, and personally id like to have seen the ERS to have been to 40 seconds with it rising to 50 seconds in 2016 and a further 2.5 seconds every year there after, with the reduction of fuel in 2016 to 90kg and 2Kg every year for 5 years.
However, the V6T era needs to have at least 9 years of free and next to open ERS development. The V6T era is all well and good, but its long term rule changes need to be worked out and properly in order for the V6Ts to work properly. At the moment i think they are a bit stillborn, and this might be what will hurt some teams and engine manufacturers over the next year or two until things get straightened out.