That's interesting about performance limitations (lack of), MarkerInbound - thanks.
Thanks also to A Squared, ethicalconundrum, and MarkerInbound for explaining the common practice of not filing ATC flight-plans for long, VFR cross-country flights in the southern US. Despite the popularity of private flying in America, no doubt the airspace in that vast continent is far less congested than in north-western Europe.
So the absence of an ATC flight-plan on this accident flight does not suggest any lack of routine flight preparation by the crew.