Here is the link to the test by Edmunds. It is not 5-10 more like 19 HP to the redline, which is quite a significant number.
But yes I absolutely agree, car magazines need to overhaul their "grading" of the vehicle.
Here are the excerpts of the dyno test.
Dyno hum
There can be no doubt that BMW's new twin-turbo 3.0-liter straight-6 engine, complete with direct injection and a high 10.2:1 compression ratio, is impressive. Two smaller snails were assigned to only three cylinders each so they'd spin up faster, reducing lag and increasing torque at low engine speeds. Boy, does it work, as this beastie is rated at 300 hp at 5,800 rpm and 300 pound-feet of torque spreading from 1,400-5,000 rpm. In a rear-drive coupe weighing in at 3,579 as-tested pounds, that sounds about right — for 5.5-second 0-60 bursts, that is.
In order to see what she's really putting out, we've brought our 335i to the chassis dynamometer at MD Automotive in Westminster, California. And since chassis dyno figures are always lower than manufacturer ratings because the former includes drivetrain losses and the latter does not, we've secured the help of an alert reader who has volunteered his month-old 335i for comparison. Steve Harrison's identically equipped 335i automatic is fresh off a trip up the California coast and all broken in. We should be able to tell if our press car's performance is unique or not.
After a short time, two sets of fresh numbers sit before us. Steve's car produces 272 rear-wheel hp at 5,970 rpm. Considering drivetrain losses, he's easily seeing the promised 300 horses at the flywheel, probably more. Our test car produces a similar 273 at 5,970. But wait, there's more: While Steve's motor gently tapers off as rpm exceeds six grand, our mill continues to make more power until it tops out at 279 at 6,295 rpm, at which point Steve's 335i lags 19 ponies behind. Notably, our car maintains its advantage for the remainder of the rev range.
So what's up?
A comparison to BMW data shows that Steve has nothing to be worried about, as his 335i's rear-wheel output curve looks about right when compared to factory flywheel data. Our car is simply stronger in such a way that makes our pavement-melting 4.8-second 0-60 more understandable. But why?
We're glad you asked. MD's dyno can also measure turbo boost during runs. It turns out that at any given rpm in the disputed region between 5,000 and 6,500, our car consistently makes about 0.5 psi more boost. Subtle, but a little goes a long way. Is this mere production variation? We can't dig deep enough to know for sure. If anything, this exercise underscores the potential of aftermarket chip tuning. Ain't electronically controlled turbo engines fun?
For the record, during a desert freeway assault to Vegas at an average speed we don't care to print, the 335i achieved 25.9 mpg, compared to a 29-mpg EPA highway rating. With a lot of city and freeway stop-and-go thrown in, the overall average drops to 20.3 — just above the 20-mpg EPA city rating. With less lead in the shoes, the EPA figures actually seem attainable.
http://www.edmunds.com/apps/vdpcontainers/...rticleId=117669