"BGP running extra light" "Below 600 Kg" blah, blah, blah.
That was what they all said before the 2004 season when the new (much lighter) 2004 Honda engine/rear end fitted in the 2003 "interim test mule" set some fast times. The new 2004 car was then launched and they continued to shake their heads in disbelief claiming that ballast was removed for PR purposes. Then, as we all know the Dave Richards run team had their best year with Button getting almost a dozen podiums. So the pre-2004 times were correct indicators.
I suspect that the BGP car is actually legit. Remember that they started well before any other team on the '09 car. Moreover, the current engine rules specify so much about the engine (bore centers, cam locations, alloys, CG height, mass, std ECU etc. that the switch to MB power was not all that shocking to their design. A few mounts here and there, maybe a custom exhaust, and you are right back where you started with the intended Honda motor.
This could be, in the immortal words of Carl Spackler, a true
"Cinderella story".
Innovation over refinement is the prefered path to performance. -- Get rid of the dopey regs in F1